Title of Invention: Labeled, Non-Peptidic, Multivalent Integrin Antagonist Compounds; Methods for Synthesis and Uses Thereof Abstract: Disclosed are multivalent, integrin-receptor antagonists that are useful in a variety of therapeutic, prophylactic, and/or diagnostic imaging modalities. In illustrative embodiments, such compounds have been prepared and utilized in the imaging, detection, localization, and/or quantitation of one or more samples of biological interest. Similarly, these compounds, as well as formulations comprising them, find utility in the prevention, treatment, and/or amelioration of one or more symptoms of a disease, abnormal condition, dysfunction, etc., including, for example proliferative diseases such as cancer in affected animals. In certain embodiments, fluorescently- or radio-labeled-non-peptidic, multivalent integrin αvβ3 compounds are provided. Compositions including such compounds have been shown to have utility in detecting, localizing, quantitating, and/or imaging integrin αvβ3 receptor-expressing cells, including, for example, cancer cells in vitro, in vivo, and/or in situ. Detailed Description: CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority to co-pending PCT Intl. Pat. Appl. No. PCT/US2012/022712, filed Jan. 26, 2012 (Atty. Dkt. No. 37182.115), which claimed priority to U.S. Provisional Patent Application No. 61/436,527 filed Jan. 26, 2011 (Atty. Dkt. No. 37182.72; now abandoned); the contents of each of which is specifically incorporated herein in its entirety by express reference thereto. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable. NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT Not Applicable. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the fields of medicine and pharmaceuticals. In particular, multivalent integrin receptor antagonists are provided, including near-infrared (NIR), fluorescent, non-peptidic, integrin αvβ3 compounds (as well as formulations and compositions thereof) that are useful in a variety of prophylactic and/or therapeutic regimens, and one or more diagnostic imaging modalities, including, for example, in the detection of mammalian cancer cells in vivo, or in situ. 2. Description of Related Art The integrins are a family of heterodimeric trans-membrane receptors each consisting of α and β subunits. To date, a total of 18 α and 8 β subunits have been discovered in mammalian cells, forming at least 24 different integrin receptors. Each integrin subunit includes a large extracellular, a single transmembrane and a short cytoplasmic domain. Based on the key roles they play in angiogenesis, leukocyte function and tumor development and their easy accessibility as cell surface receptors interacting with extracellular ligands, the integrin superfamily, integrin αvβ3 in particular, have been extensively investigated as imaging and chemotherapy targets (Chen, 2011). Integrin αvβ3 is a receptor for extracellular proteins including vitronectin, fibronectin and fibrinogen that contain an arginine-glycine-aspartic acid (RGD) sequence (DeNardo et al., 2000; Janssen et al., 2004). RGD peptides specific binding to αvβ3 receptor have been labeled with various gamma and positron emitters for scintigraphic detection (Chen et al., 2004; Harris et al., 2003; Haubner et al., 2004; Haubner et al., 1999; van Hagen et al., 2000) and gamma and beta emitters for radiotherapy of tumors (Bernard et al., 2004; Capello et al., 2004; DeNardo et al., 2000; Janssen et al., 2004; Onthank et al., 2004). Steady progress has been reported in optimizing the labeling methodologies to increase tumor-to-nontumor tissue ratios, especially the tumor-to-liver and tumor-to-kidney ratios by increasing the hydrophilicity of the product via glycosylation and PEGylation of radiolabeled RGD peptides (Chen et al., 2004a; Chen et al., 2004b; Chen et al., 2004; Haubner et al., 2001). Dimeric and tetrameric RDG peptides labeled with 18F and 64Cu were prepared for positron emission tomography (PET) imaging for cancer diagnosis (Chen et al., 2004b; Chen et al., 2005; Wu et al., 2005). It was reported that these oligomeric RDG peptides enhanced the receptor-binding affinity, thereby improving the tumor targeting and slowing the wash-out of radioactivity from tumor. Receptors on the surfaces of mammalian cells participate in many biological cellular processes, including, for example, cell proliferation and invasion. One particular receptor that has implications for a wide variety of disease conditions is the vitronectin receptor αvβ3. A member of the integrin superfamily of receptors, αvβ3 is found in various cells including angiogenic endothelia and osteoclasts. Integrins have been implicated in a variety of disorders and diseases and disorders, including, cancer and inflammation, as well as autoimmune and genetic diseases and disorders. αvβ3 plays a critical in vivo role in endothelial cell survival during angiogenesis, and also potentiates the internalization of various cellular viruses including, rotavirus, adenovirus, and foot-and-mouth disease virus. Development of antagonists of the integrin αvβ3 receptor have been described, and monovalent integrin αvβ3 receptor antagonists having a tetrahydropyridi-midinylaminoethyloxybenzoyl group conjugated to a sulfonylamino-β-alanine nucleus have been synthesized as noted in U.S. Pat. Appl. Publ. No. 2006/0030575 (specifically incorporated herein in its entirety by express reference thereto). The development of multivalent integrin αvβ3 antagonists, have not, however, been reported. Thus, there is a need in the art to develop new, improved integrin antagonist compounds that (1) bind to αvβ3 integrin receptors with higher specificity and/or higher affinity than existing compounds; (2) bind to selected target cells (such as, for example, mammalian tumor cells) with high affinity, and with substantial specificity; and (3) are more resistant to cleavage and/or degradation from one or more endogenous or exogenous proteases (including, for example, those found in plasma, the gastrointestinal tract, tumor cells, and other mammalian tissues). BRIEF SUMMARY OF THE INVENTION The present invention provides new and useful compositions, as well as methods of employing them that may advantageously improve delivery of therapeutic, diagnostic and/or prophylactic agents to an animal in need thereof. In an important embodiment, the invention provides a bifunctional compound that includes a first targeting moiety defined as a synthetic or semisynthetic, small-molecule, peptidomimetic, multivalent integrin αvβ3 antagonist moiety that is operably linked to at least one detectable moiety, at least one therapeutic agent, or any combination thereof. In particular aspects, the multivalent integrin αvβ3 antagonist moiety is characterized as a bivalent, a trivalent, a tetravalent, a pentavalent, a hexavalent, or a heptavalent integrin αvβ3 antagonist moiety and in particular embodiments includes the formula of one or more of the following antagonist moieties: In particular embodiments, the integrin αvβ3 antagonist moiety has the formula: 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-(S)-aminoethyl sulfonyl-amino-β-alanine. In the practice of the invention, the detectable moiety includes one or more detectable labels such as a near-infrared label, a fluorescent label, a radiolabel, a magnetic spin resonance label, a chromophore, or any combination thereof. Exemplary labels include, without limitation, fluorescent labels such as fluorescein, rhodamine, Texas Red, a Cy2, moiety, a Cy3 moiety, a Cy5 moiety, a Cy 5.5 moiety, or a Cy 7 moiety, a cyanine dye, or a derivative or any combination thereof. In the case of radiolabel compounds, the molecule may include 18F, 64Cu, or a combination thereof. The bifunctional compounds of the invention may be synthesized with one or more linker moieties, including without limitation, PEG, tri(ethylene glycol), tetra(ethylene glycol), n-(ethylene glycol), where n is from 3 to 12, 2-aminooctanedioic acid, triethanolamine, or any combination, analog, or derivative thereof. In the practice of the various diagnostic and therapeutic methods described herein, the bifunctional compounds of the invention are preferably formulated within a pharmaceutically-acceptable diluent, buffer, or vehicle, and particularly ones that are suitable for administering the bifunctional compounds to a mammal, such as a human patient in need thereof. The bifunctional compounds of the invention may be included within a nanoparticle, a microparticle, a nanocapsule, a microbubble, a microcapsule, a nanosphere, or a microsphere, or any combination thereof; or (b) further comprising a surfactant, a neutral lipid, a lipid complex formed from at least two distinct lipids, a liposome, a niosome, an ethosome, a transferosome, a phospholipid, a sphingosome, or any combination thereof, and in particular therapeutic and diagnostic modalities, may be preferably formulated within a nanoparticle delivery system, such as a polymerized, liposomal-based, nanoparticle delivery system. Such formulations of the present invention may optionally include, one or more neutral lipids (including, without limitation, one or more of a cephalin, a ceramide, a cerebroside, a cholesterol, a diacylglycerol, a diacylphosphatidylcholine, a diacylphosphatidylethanolamine, a phosphatidylcholine, a phosphatidylethanolamine, a sphingolipid, a sphingomyelin, a tetraether lipid), as well as combinations and derivatives thereof. In an exemplary illustrative embodiment, the bifunctional compound has the chemical formula: When used as a therapeutic delivery vehicle, the compounds of the invention will preferably include at least one therapeutic agent (including, without limitation, one or more of an antineoplastic agent, an immunomodulating agent, a neuroactive agent, an anti-inflammatory agent, an anti-lipidemic agent, a hormone, a hormone receptor, a receptor agonist, a receptor antagonist, an anti-infective agent, or a compound selected from a protein, a peptide, an antibody, an enzyme, an RNA, a DNA, an siRNA, an mRNA, an RNAi, a ribozyme, a cofactor, a steroid, an antisense oligonucleotide, a detection agent, an imaging agent, a contrast agent, a gas, a pharmaceutically-active molecule, a targeting moiety, a linker, and any combinations thereof). In exemplary illustrative embodiments, the bifunctional compound includes the antineoplastic agent doxorubicin. The invention also provides a method for treating or ameliorating at least one symptom of a disease, dysfunction, or abnormal condition in a mammal. The method, in an overall and general sense, includes at least the step of providing to the mammal one or more of the bifunctional therapeutic integrin-receptor antagonist compounds disclosed herein, in an amount, and for a time sufficient to treat or ameliorate the at least one symptom of the disease, dysfunction, or abnormal condition in the mammal. The invention further provides a method of detecting or imaging of a population of integrin receptor-presenting cells within or about the body of an animal. In an overall and general sense, this method includes at least the step of providing or administering to one or more cells, tissues, or organs of the animal at least one of the bifunctional therapeutic compounds disclosed hererin, in an amount and for a time sufficient to detect or image at least a first portion of the population of integrin receptor-presenting cell in the mammal to which the detectable moiety is bound. In exemplary embodiments, the detectable moiety is identifiable by confocal microscopic imaging, CT imaging, PET imaging, MRI, or any combination thereof. In another embodiment, the invention provides a method for imaging a first population of integrin αvβ3-expressing cells within or about the body of an animal. In an overall and general sense, the method includes administering to the animal an amount of one or more of the bifunctional compounds disclosed herein, for a time effective to image the first population of integrin αvβ3-expressing cells within or about the body of the animal. The integrin αvβ3-expressing cells may typically include one or more cancer cells, one or more tumor cells, one or more hyperproliferative cells, or any combination thereof. In particular embodiments, one or more of the population of targeted cells will express at least a first integrin αvβ3 receptor on its cell surface, to which the bifunctional compound is localized by virtue of its integrin-targeting moiety. In the practice of the method, the animal recipient may be a mammal, including a human, that is suspected of having, diagnosed with, or at risk for developing one or more cancers, tumors, or such like. In certain embodiment, the first population of integrin αvβ3-expressing cells, or the first population of tumor cells is located within or about the body of a mammalian patient, and the method comprises systemically or directly administering an effective amount of one or more of the therapeutic bifunctional compounds disclosed herein to the mammalian patient for an period to treat, lessen, or ameliorate one or more symptoms of the disease. In diagnostic modalities, the detectable moiety is preferably an imaging moiety that is useful in one or more diagnostic methodologies such as microscopic imaging, near-IR microscopic imaging, fluorescent microscopic imaging, confocal microscopic imaging, or any combination thereof. In particular, a new class of integrin receptor antagonists has now been discovered that advantageously displays high binding affinity, specificity for integrin αvβ3, and inherent stability. These ligands are particularly useful for imaging of tumor, organs, and/or tissues, as well as for treating or ameliorating one or more symptoms of cancer, inflammatory disease, autoimmune disease, and the like. Pharmaceutical formulations and kits containing these new compounds, suitable for imaging, diagnosis, prophylaxis, and/or therapy are also provided. The present invention resides in these compounds themselves, and in pharmaceutical compositions containing one or more of the compounds together with a pharmaceutically acceptable carrier. The invention also encompasses the administration of such compound(s) or pharmaceutical compositions including the compounds to mammals afflicted with a condition that is mediated at least by a multivalent (i.e., polyvalent) integrin receptor, and most notably αvβ3, as treatment for the condition. Exemplary multivalent compounds include, but are not limited to, bivalent, trivalent, tetravalent, pentavalent, hexavalent, and heptavalent integrin receptor antagonists, and the like. In particularly exemplary embodiments described herein, bivalent integrin receptor antagonists were shown to be particularly useful in the practice of the methods described herein, although other polyvalent compounds are contemplated to be similarly useful, and in certain applications, may demonstrate superior results than those illustrated herein for the bivalent test compound described in the following illustrative examples. The invention further encompasses the administration of the imaging agents that contain such compound(s) linked to a detectable moiety, or pharmaceutical compositions of such imaging agents, as part of the imaging of multivalent integrin receptor cells, again most notably αvβ3-bearing cells, in the mammal. As will be noted from the description below, this invention further encompasses treatment and prevention of various disease conditions, symptoms thereof, or both, that are associated with the biological activity of one or more multivalent integrin receptors, most notably αvβ3, by either blocking (i.e., inhibiting, the receptor), or by modifying cells that bear one or more such receptors on or about their cell membranes or on at least a first portion of their cellular surface, such that delivery of one or more polynucleotides or polypeptides of interest may be delivered to the cells as a result of the binding of the disclosed delivery agents to such receptors, thereby permitting uptake or introduction of the target molecule to the selected cells of interest by employing one of the multivalent integrin antagonist delivery agents. In an overall and general sense, the invention provides small-molecule compounds (and particularly non-peptidic, polyvalent/multivalent integrin antagonist compounds), as well as compositions and formulations comprising them, that are useful in a variety of medical imaging, diagnostic, prophylactic, and therapeutic regimens. In a first embodiment, the invention provides non-peptidic (i.e., “small molecule”) integrin antagonist compounds, and preferably one or more polyvalent compounds (e.g., one or more bivalent, trivalent, tetravalent, pentavalent, hexavalent, heptavalent, etc.) that specifically target, specifically bind to, and/or specifically uptaken by one or more particular mammalian cell surface receptors. In illustrative embodiments, these mammalian cell surface receptors include human receptors such as the integrin αvβ3 receptor. In exemplary embodiments, the invention provides a bivalent, integrin αvβ3 antagonist-moiety-containing bifunctional compound, the targeting moiety having the structural formula of one or more of the following compounds: In certain embodiments, a bifunctional integrin αvβ3 antagonist moiety-containing molecule preferably includes at least a first imaging moiety that includes at least a first detectable label, such as, without limitation, a fluorescent label such as the Cy5.5 moiety. In exemplary embodiments, the bifunctional molecules include a bivalent integrin αvβ3 antagonist compound operably linked to a first reporter molecule (such as a fluorescent moiety such as Cy5.5), wherein the labeled compound has the formula: As noted herein, in certain embodiments, the disclosed integrin antagonist compounds of the invention are formulated as a pharmaceutical composition, that may include one or more pharmaceutically-acceptable buffers, diluents, vehicles, and the like. Likewise, in the practice of the invention, it may be desirable to formulate the integrin antagonist compounds of the invention by the addition of one or more surfactants, neutral lipids (including, without limitation, one or more cephalins, ceramides, cerebrosides, cholesterols, diacylglycerols, diacylphosphatidylcholines, diacylphosphatidylethanolamines, phosphatidylcholines, phosphatidylethanolamines, sphingolipids, sphingomyelins, tetraether lipids, or any combination thereof), lipid complexes (including, e.g., those formed from two or more distinct lipids), liposomes, niosomes, ethosomes, transferosomes, phospholipids, sphingosomes, or any combination thereof. Optionally, the compounds of the invention may be formulated into compositions that are comprised within one or more nanoparticles, microparticles, nanocapsules, microcapsules, nanospheres, or microspheres, or any combination thereof. Preferred pharmaceutical composition of the present invention also include those that further comprise one or more of an antineoplastic agent, an immunomodulating agent, a neuroactive agent, an antiflammatory agent, an antilipidemic agent, a hormone, a receptor agonist or antagonist, or an antiinfective agent, or a compound selected from a protein, a peptide an antibody, an enzyme, an RNA, a DNA, an siRNA, an mRNA, a ribozyme, a hormone, a cofactor, a steroid, an antisense molecule, a detection agent, an imaging agent, a contrast agent, a gas, and a pharmaceutically-active molecule. Preferably, the compounds, compositions, and pharmaceutical formulations of the present invention are formulated for administration to an animal host cell, and to mammalian host cells, such as human host cells, in particular. The multivalent, integrin antagonist compounds of the present invention (as well as compositions and formulations comprising one or more of them) find particular utility in diagnosis (including, without limitation, in the diagnosis of a disease, disorder, dysfunction, abnormal condition, trauma, or one or more symptoms thereof), in medical imaging (including, without limitation, in one or more confocal microscopic imaging modalities), or in the prophylaxis or therapy of one or more diseases, dysfunctions, disorders, or abnormal conditions in an animal (including, without limitation, in a mammal such as a human). The invention also provides use of one or more of the disclosed compounds in the manufacture of a medicament for the medical imaging, diagnosis, or treatment of one or more hyperproliferative disorders, including, without limitation, cancer and such like. The invention further provides use of one or more of the disclosed compounds in the manufacture of a diagnostic imaging agent, and particularly NIR fluorescently labeled integrin antagonist compounds useful in confocal microscopy and other medical imaging modalities. The invention also provides a method of treating a mammal that is afflicted with a condition that is mediated by an integrin receptor. In an overall and general sense, such a method generally involves administering to a mammal in need thereof, an amount of one or more of the disclosed integrin antagonist compounds, in an amount and for a time sufficient to treat or ameliorate one or more symptoms of such a condition. A further aspect of the invention is a method of imaging cells, organs, and/or tissues about or within the body of an animal that express one or more integrin receptor-presenting cells. In an overall sense, the method typically involves providing to a mammalian patient in need thereof, a first detectably-labeled integrin antagonist compound in an amount and for a time sufficient to image such cells, organs, and/or tissues. In related embodiments, the invention also provides a method of imaging one or more tumors, or pluralities of tumor cells, in a patient afflicted with, suspected of having, or diagnosed with, one or more hyperproliferative diseases (e.g., tumor growth). In an overall and general sense, such a method typically involves administering to, or providing a patient in need thereof, with an amount of one or more of the disclosed labeled integrin antagonist compounds and for a time effective to facilitate the imaging of one or more such tumors or integrin receptor presenting cells in the patient. In certain embodiments, the integrin antagonist compound is labeled with a detectable moiety, and preferably a near-infrared fluorescent moiety, such as a Cy5.5 label and the like, or a radiolabeled moiety, including, without limitation, an 18F or a 64Cu moiety. In exemplary embodiments, the tumor cells to be identified using the disclosed methods will preferably express one or more integrin αvβ3 receptors on or about the surface of at least a first population of tumor cells, such that the compounds of the invention may selectively “target” those tumor cells by virtue of the antagonist moiety binding to its corresponding surface-expressed receptor. In another embodiment, the invention provides methods for imaging one or more populations of integrin αvβ3-expressing cells within or about the body of a mammalian patient, or for targeting to such cells, one or more therapeutic, diagnostic, or prophylactic reagents. In an overall sense, such methods generally involve providing to the patient at least a first labeled integrin antagonist composition as disclosed herein, in an amount and for a time sufficient to image the one or more populations of such integrin αvβ3-expressing cells within or about the body of the mammalian patient. Such a method preferably includes one or more optical imaging techniques such as near-infrared fluorescent confocal microscopy or such like. In particular embodiments, the present invention provides for the use of one or more of the disclosed multivalent integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, in the manufacture of a medicament for diagnosis, prophylaxis, therapy, or medical imaging, and particularly for use in the manufacture of a medicament for imaging, diagnosing, treating, and/or preventing one or more diseases, dysfunctions, or disorders in a mammal, or a symptom thereof, or a combination of the foregoing, and in a human in particular. The present invention also provides for the use of one or more of the disclosed multivalent integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, in the manufacture of a medicament for the medical imaging, diagnosis, prophylaxis and/or therapy of one or more medical conditions, including, for example, cancer; diabetes; neurological disorders; cerebrovascular accidents; stroke, ischemia, infarction, aneurysm, musculoskeletal deficiencies; neuromuscular disorders; osteogenic diseases peptide, polypeptide, or enzyme deficiencies; hormone, cofactor, or trophic factor deficiencies; one or more cardiovascular and/or cardiocirculatory diseases, disorders, or dysfunctions; organ disease, dysfunction, or failure; genetic disorders; congenital abnormalities, defects, or malformations; trauma; and the like. The present invention also provides for the use of one or more of the disclosed multivalent integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, in the manufacture of a medicament for the prevention of disease, including, in the preparation of one or more vaccines suitable for prophylactic administration. Those of ordinary skill in the art will appreciate from the present disclosure that the integrin antagonist compounds of the invention may also be co-administered with one or more additional prophylactic and/or therapeutic agents for the prevention, treatment, and/or amelioration of one or more symptoms of hyperproliferative, inflammatory, and/or autoimmune diseases, and the like. Suitable anti-inflammatory agents for combination therapy include, without limitation, corticosteroids, non-steroidal anti-inflammatory agents, antibodies such as infliximab, 5-aminosalicylates, antibiotics, pharmaceutically acceptable salts thereof; derivatives thereof, prodrugs thereof, and combinations thereof. Suitable immunosuppressive agents for combination therapy include, without limitation, azathioprine and metabolites thereof, anti-metabolites such as methotrexate, immunosuppressive antibodies, mizoribine monophosphate, cyclosporine, scoparone, rapamycin, glatiramer acetate, mycopehnolate, pharmaceutically acceptable salts thereof, derivatives thereof, prodrugs thereof, and combinations thereof. The invention also provides methods for providing a therapeutic, prophylactic, or diagnostic compound to a first cell in a mammal, with the method generally including providing to a mammal in need thereof, an effective amount of a bifunctional multivalent integrin αvβ3 antagonist composition that is operably linked to at least one therapeutic, prophylactic, and/or diagnostic moiety, and for a time effective to provide the desired therapy, prophylaxis or diagnosis in one or more cells and/or tissues of the selected mammal receiving the compound(s). In certain aspects of the invention, the invention provides integrin antagonist compositions (and multivalent integrin αvβ3 antagonist compositions in particular), for delivering one or more compounds to a host cell. In particular embodiments, the host cell is preferably a mammalian host cell, and one that expresses an integrin receptor, such as the integrin αvβ3 receptor. In certain preferred embodiments of the invention, the host cell is a human cell. In other preferred aspects, the host cell is included within the body of a human, or included within at least a first ex vivo tissue or plurality of cells that are compatible for implantation into the body of such a human as part of a typical ex vivo therapy protocol or such like. In other aspects of the invention, integrin antagonist compositions, and integrin αvβ3 antagonist compositions in particular, are provided that may further optionally include one or more additional distinct components, including, without limitation, one or more therapeutics, one or more diagnostics, or one or more imaging compounds, or any combination thereof. Similarly, the disclosed integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, may also be formulated in association with one or more additional vehicles for delivering an agent to an animal, including, for example, fully-polymerized liposomes, partially-polymerized liposomes, cross-linked lipids, unpolymerized liposomes, niosomes, transferosomes, ethosomes, phospholipid complexes, lipid particles, lipid vesicles, nanoparticles, microparticles, nanocapsules, microcapsules, microspheres, nanospheres, sphingosomes, and such like. In certain embodiments, the antagonist compositions of the present invention can be formulated with one or more surfactants, neutral lipids, lipid complexes, liposomes, niosomes, ethosomes, transferosomes, phospholipids, sphingosomes, or any combination thereof. Exemplary neutral lipids include, without limitation, a cephalin, a ceramide, a cerebroside, a cholesterol, a diacylglycerol, a diacylphosphatidylcholine, a diacylphosphatidylethanolamine, a phosphatidylcholine, a phosphatidylethanolamine, a sphingolipid, a sphingomyelin, a tetraether lipid, or any combination thereof. In certain embodiments, the integrin antagonist compositions of the present invention may be comprised within a liposome, a nanoparticle, a microparticle, a nanocapsule, a microcapsule, a nanosphere, or a microsphere, or any combination thereof. Methods for the preparation of liposomal formulations are known to those of ordinary skill in the molecular pharmaceutical arts. Liposomes, for example, may be formed by any conventional technique, including without limitation, by extrusion, sonication, or mechanical shearing, or a combination thereof. Entrapment of the antagonist compositions (optionally together with one or more additional active ingredient [s]) into suitable lipid vesicles may also be accomplished by any conventional technique, including, without limitation, exposure of the lipid vesicles to UV light in the presence of the active ingredient(s). The compositions of the present invention may also be delivered to cells in association with one or more conventional pharmaceutical compounds or compositions, which preferably may provide diagnosis, prophylaxis, and/or treatment of the same (or different) type as provided by the multivalent integrin antagonist composition itself. Therapeutic, Prophylactic and Diagnostic Methods Another important aspect of the present invention concerns methods for using the disclosed multivalent integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, to treat or ameliorate the symptoms of one or more diseases, dysfunctions, or deficiencies in an animal, and preferably in a mammal such as a human. Such methods generally involve administration to the animal in need thereof, one or more of the disclosed antagonist compounds or compositions, in an amount and for a time sufficient to treat or ameliorate the symptoms of such a deficiency in the affected animal. The methods may also encompass prophylactic treatment of animals suspected of having such conditions, or administration of such compositions to those animals at risk for developing such conditions either following diagnosis, or prior to the onset of symptoms. As such, preferred animals for administration of the pharmaceutical compositions disclosed herein include mammals, and particularly humans. Other preferred animals include non-human primates, bovines, ovines, caprines, lupines, equines, porcines, canines, and felines, as well as animals under the care of a veterinary practitioner. Pharmaceutical Formulations In certain embodiments, the present invention concerns formulation of one or more therapeutic or diagnostic agents in a pharmaceutically acceptable composition for administration to a cell or an animal, either alone, or in combination with one or more other modalities of diagnosis, prophylaxis, and/or therapy. The formulation of pharmaceutically-acceptable excipients and carrier solutions is well known to those of ordinary skill in the art, as is the development of suitable dosing and treatment regimens for using the particular compositions described herein in a variety of diagnostic and therapeutic regimens. In certain circumstances it will be desirable to deliver the compositions of the present invention in suitably-formulated pharmaceutical vehicles by one or more standard delivery techniques or routes of administration, including, for example, subcutaneously, intraocularly, intravitreally, parenterally, intravenously, intracerebroventricularly, intramuscularly, intrathecally, orally, intraperitoneally, transdermally, topically, by oral or nasal inhalation, or by direct injection to one or more cells, tissues, or organs. The methods of administration may also include those modalities as described in U.S. Pat. Nos. 5,543,158; 5,641,515, and 5,399,363, each of which is specifically incorporated herein in its entirety by express reference thereto. Solutions of the active compounds as freebase or pharmacologically acceptable salts may be prepared in sterile water, and may be suitably mixed with one or more surfactants, such as hydroxypropylcellulose. Dispersions may also be prepared in glycerol, liquid polyethylene glycols, oils, or mixtures thereof. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. For administration of an injectable aqueous solution, for example, the solution may be suitably buffered, if necessary, and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous, and intraperitoneal administration. For such preparations, any available sterile aqueous medium can be employed as will be known to those of ordinary skill in the art in light of the present disclosure. For example, one dosage may be dissolved in 1 mL of isotonic NaCl solution, and either added to 1000 mL of hypodermoclysis fluid or injected at the proposed site of infusion (see, for example, “Remington's Pharmaceutical Sciences” 15th Edition, pages 1035-1038 and 1570-1580). Some variation in dosage will necessarily occur depending on the condition of the subject being treated and other known dosing factors. The person responsible for administration will determine, in any event, the appropriate dose for the individual subject. Moreover, for human administration, preparations should meet sterility, pyrogenicity, and the general safety and purity standards as required by FDA Office of Biologics standards. Sterile injectable compositions may be prepared by incorporating the disclosed integrin antagonist compounds in the required amount in the appropriate solvent with several of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions can be prepared by incorporating the selected sterilized active ingredient(s) into a sterile vehicle including the basic dispersion medium and other ingredients as needed from those discussed herein. The integrin antagonist compositions, and in particular, the multivalent integrin αvβ3 antagonist compositions disclosed herein, may also be optionally formulated in one or more neutral or salt form(s). Pharmaceutically-acceptable salts include the acid addition salts (formed with the free amino groups of the protein), and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine, and the like. Upon formulation, solutions will be administered in a manner compatible with the dosage formulation, and in such amount as is effective for the intended application. The formulations are readily administered in a variety of dosage forms such as injectable solutions, topical preparations, oral formulations, including sustain-release capsules, hydrogels, colloids, viscous gels, transdermal reagents, intranasal and inhalation formulations, and the like. The amount of integrin antagonist compositions, and multivalent integrin αvβ3 antagonist compositions in particular, as well as the time or duration needed for the administration of such composition(s), will be within the purview of the ordinary-skilled artisan particularly given the benefit of the present teachings. It is likely, however, that the administration of a therapeutically-effective, pharmaceutically-effective, prophylactically-effective, and/or diagnostically-effective amount of the disclosed multivalent integrin antagonist compositions may be achieved by a single administration, such as for example, a single injection of a sufficient quantity of the delivered agent to provide the desired benefit to the patient undergoing such a procedure. Alternatively, in some circumstances, it may be desirable to provide multiple, or successive, administrations of the multivalent integrin antagonist compositions, either over a relatively short, or even a relatively prolonged period of time, as may be determined by the medical practitioner overseeing the administration of such compositions to the selected individual. Typically, formulations of one or more active ingredients in the pharmaceutical formulations disclosed herein will contain an effective amount of the integrin antagonist compound for the selected therapy, prophylaxis, diagnosis, and/or imaging (e.g., a prophylactically-, therapeutically-, diagnostically-, or imaging-effective amount). Preferably, the formulation may contain at least about 0.1% of each active ingredient, although the percentage of the active ingredient(s) may, of course, be varied, and may conveniently be present in amounts from about 0.5 to about 80 weight % or volume %, or from about 1 to about 70 weight % or volume %, or more preferably, from about 2 to about 50 weight % or volume %, based upon the total formulation. Naturally, the amount of active compound(s) in each composition may be prepared in such a way that a suitable dosage will be obtained in any given unit dose of the compound. Factors such as solubility, bioavailability, biological t1/2, route of administration, product shelf life, as well as other pharmacological considerations will be contemplated by one of ordinary skill in the art of preparing such pharmaceutical formulations, and as such, a variety of dosages and treatment regimens may be desirable. In one embodiment, administration may be parenterally, intravenously, intramuscularly, or even intraperitoneally. The pharmaceutical forms adapted for injectable administration include sterile aqueous solutions or dispersions, and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions including without limitation those described in U.S. Pat. No. 5,466,468, which is specifically incorporated herein in its entirety by express reference thereto). In all cases, the form must be sterile and must be fluid to facilitate syringability. Such a dosage form must be at least sufficiently stable under the conditions of manufacture and storage, and must be preserved against the contaminating action of microorganisms, such as viruses, bacteria, fungi, and such like. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (e.g., glycerol, propylene glycol, and liquid polyethylene glycol, and the like, or a combination thereof), one or more vegetable oils, or any combination thereof, although additional pharmaceutically-acceptable components may be included. It is contemplated that formulations of the disclosed multivalent integrin antagonist compositions may be suitable for direct injection into one or more organs, tissues, or cell types in the body. Such injection sites include, but are not limited to, the circulatory system, the spinal cord, the lymphatic system, a joint or joint capsule, a synovium or subsynovium tissue, tendons, ligaments, cartilages, bone, periarticular muscle or an articular space of a mammalian joint, as well as direct administration to an organ or tissue site such as the heart, liver, lung, pancreas, intestine, brain, bladder, kidney, or other site within the patient's body, including, for example, introduction of the delivered therapeutic or diagnostic agent(s) via intra-abdominal, intra-thoracic, intravascular, or intracerebroventricular delivery of a suitable formulation. Administration of the disclosed compositions need not be restricted to one or more of these delivery routes, but instead may be conducted using suitable techniques, including those known to the one of ordinary skill in the relevant medical arts. In certain embodiments the active ingredients of the invention may be formulated for delivery by needle, catheter, and related techniques, or alternatively, may be included within a medical device, including, for example, drug-eluting implants, stents, catheters, and such like. The formulations may also be prepared for injection by an implanted drug-delivery pump or similar mechanism. The administration of the disclosed pharmaceutical compositions by intranasal sprays, inhalation, and/or other aerosol delivery vehicles is also contemplated. Methods for delivering peptide and non-peptidic compositions directly to the lungs via nasal aerosol sprays have been described e.g., in U.S. Pat. Nos. 5,756,353 and 5,804,212, each of which is specifically incorporated herein in its entirety by express reference thereto. Delivery of drugs using intranasal microparticle resins (see e.g., Takenaga et al., 1998) and lysophosphatidyl-glycerol compounds (U.S. Pat. No. 5,725,871, specifically incorporated herein in its entirety by express reference thereto) are also well-known in the pharmaceutical arts. Likewise, transmucosal drug delivery in the form of a polytetrafluoroethylene support matrix is suitable in the practice of the invention, and is described in U.S. Pat. No. 5,780,045 (specifically incorporated herein in its entirety by express reference thereto). The disclosed multivalent integrin antagonist compositions may also be administered through transdermal or other topical administration routes. Exemplary methods for the use of disclosed formulations in topical therapy are found, for example, in U.S. Pat. Nos. 5,540,936, and 6,133,451, each of which is specifically incorporated herein in its entirety by express reference thereto. In particular embodiments, the disclosed multivalent integrin antagonist compositions can be formulated using one or more pharmaceutical buffers, vehicles, or diluents, and intended for administration to a mammal through suitable techniques, such as, by intramuscular, intravenous, subcutaneous, intrathecal, intra-abdominal, intravascular, intra-articular, or alternatively, by direct injection to one or more cells, tissues, or organs of such a mammal. The multivalent integrin antagonist formulations disclosed herein are useful in any animal, and are not in any way limited to use only in humans, or even to primates, or mammals. In preferred embodiments, however, the compositions of the present invention may be formulated for administration to a mammal, including humans, for a variety of diagnostic, therapeutic, and/or prophylactic regimens. Such compositions may also be provided in excipient formulations that are acceptable for veterinary administration, including, for example, to selected livestock, exotic or domesticated animals, companion animals (including pets and such like), non-human primates, as well as zoological or otherwise captive specimens, and such like. Such methods may also encompass prophylactic treatment of one or more animals suspected of having, or at risk for developing one or more such conditions either following diagnosis, or prior to the onset of symptoms. To that end, in certain embodiments the multivalent integrin antagonist compositions disclosed and/or described herein may also find utility in the area of vaccine development, antigen administration, vaccination, and such like. Kits Kits including one or more of the disclosed multivalent integrin antagonist compositions or pharmaceutical formulations including such; and instructions for using the kit in a therapeutic, prophylactic, diagnostic, and/or other clinical embodiment also represent preferred aspects of the present disclosure. Such kits may further include one or more of the disclosed multivalent integrin antagonist compositions, either alone, or in combination with one or more additional prophylactic, therapeutic or diagnostic compounds, or one or more pharmaceuticals, and such like. The kits of the invention may be packaged for commercial distribution. They may also further optionally include one or more devices for delivering the multivalent integrin antagonist compositions to an animal (e.g., syringes, injectables, and the like). Such kits may be therapeutic kits for treating, preventing, or ameliorating the symptoms of a disease, deficiency, dysfunction, and/or injury, and may include one or more of the multivalent integrin antagonist compositions, and instructions for using the kit in a therapeutic, prophylactic, diagnostic, and/or medical imaging regimen. The container for such kits may typically include at least one vial, test tube, flask, bottle, syringe or other container, into which the composition(s) may be placed, and preferably suitably aliquotted. Where a second composition is also provided, the kit may also contain a second distinct container into which this second composition may be placed. Alternatively, the plurality of compositions may be prepared and packaged in a single container, such as a vial, flask, syringe, catheter, cannula, bottle, or other suitable single container or delivery device. The kits of the present invention may also typically include a retention mechanism adapted to contain or retain the vial(s) or other container(s) in close confinement for commercial sale, such as, e.g., injection or blow-molded plastic containers into which the desired vial(s) or other container(s) may be retained to minimize or prevent breakage, exposure to sunlight, or other undesirable factors, or to permit or facilitate ready use of the composition(s) included within the kit. Alternatively, such kits may be prepared that include at least one pharmaceutical formulation as disclosed herein and instructions for using the composition in diagnosis and/or for one or more medical imaging modalities. The container for such kits may typically include at least one vial, test tube, microcentrifuge tube, or other container, into which the multivalent integrin composition(s) may be placed and suitably aliquotted. Where a radiolabel or fluorigenic label, or other such detecting component, is included within the kit, the labeling agent may be provided either in the same container as the multivalent integrin antagonist composition, or may alternatively be placed in a second distinct container into which this second composition may be placed and suitably aliquotted. Alternatively, the multivalent integrin antagonist compositions may be prepared in combination with one or more additional reagents in a single container, and in most cases, the kit will also typically include a retention mechanism adapted to retain or contain the vial(s) or other container(s) in close confinement for commercial sale and/or convenient packaging and delivery to minimize or avoid any undesirable environmental factors. Compositions for the Preparation of Medicaments Another important aspect of the present invention concerns methods for using the disclosed compositions (as well as formulations including them) in the preparation of medicaments for preventing, treating or ameliorating the symptoms of various diseases, dysfunctions, or deficiencies in an animal, such as a vertebrate mammal. Use of the disclosed compositions is also contemplated in therapy and/or prophylaxis of one or more diseases, disorders, dysfunctions, conditions, disabilities, deformities, or deficiencies, or any symptom thereof, particularly when the multivalent integrin antagonist composition is formulated to include one or more therapeutic (or prophylactic) agents known to one of ordinary skill in the medical arts. Such use generally involves administration to an animal in need thereof one or more of the disclosed compositions that include at least a first therapeutic or prophylactic agent, in an effective amount and for a time sufficient to prevent, treat, lessen, or ameliorate one or more symptoms of such a disease, disorder, dysfunction, condition, disability, deformity, or deficiency in the affected animal. Compositions including one or more of the disclosed formulations also form part of the present invention, and particularly compositions that further include at least a first pharmaceutically-acceptable excipient for use in the therapy, prophylaxis, or diagnosis of one or more diseases, dysfunctions, disorders, or such like. Use of the disclosed multivalent integrin antagonist compositions is also contemplated, particularly in the manufacture of one or more medicaments and methods involving one or more therapeutic (including chemotherapy, phototherapy, laser therapy, etc.), prophylactic (including e.g., vaccines), or diagnostic regimens (including, e.g., in diagnostic imaging such as radiology, scintigraphy, microscopy (including, without limitation, confocal laser-scanning microscopy), ultrasound, PET, CT, MRI, and the like). Such multivalent integrin antagonist formulations may optionally further include one or more additional distinct reagents, such as a diagnostic reagent, a lipid, lipid complex, phospholipid, a liposomal delivery formulation, or any other such vehicle(s), additive(s) and/or adjuvant(s) as may be suitable for administration of the multivalent integrin antagonist composition to an animal in need thereof. Such routes of administration are known to and may be selected by those of ordinary skill in the art, and include, for example, but are not limited to, delivery routes including intramuscular, intravenous, intra-arterial, intrathecal, intracavitary, intraventricular, subcutaneous, or direct injection into an organ, tissue site, or population of cells in the recipient animal, or other routes noted herein. BRIEF DESCRIPTION OF THE DRAWINGS For promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one of ordinary skill in the art to which the invention relates. The following drawings form part of the present specification and are included to demonstrate certain aspects of the present invention. The invention may be better understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: FIG. 1A illustrates the chemical structure of compound (1) IA in accordance with one aspect of the present invention; FIG. 1B shows an illustrative synthetic reaction scheme of bivalent compound (3) IA in accordance with one aspect of the present invention; FIG. 2 illustrates the chemical structure of bivalent-IA-Cy5.5 conjugate in accordance with one aspect of the present invention; FIG. 3A and FIG. 3B schematically illustrate the lowest-energy conformation of bivalent-IA-Cy5.5 conjugate (FIG. 3A) and interaction of bivalent-IA-Cy5.5 with integrin (FIG. 3B). The lowest-energy conformation was obtained from the analysis of molecular dynamics trajectories. The integrin structure was obtained from the open form of the integrin crystal structure (1JV2); FIG. 4 shows results of an enzyme-linked immunosorbent assay (ELISA) of IA (IC50: 22.33±4.51 nM), bivalent IA (IC50: 0.40±0.11 nM), bivalent-IA-Cy5.5 conjugate (IC50: 0.13±0.02 nM), and c-[RGDfV] (IC50: 4.80±3.01 nM). In this representative study, all data points were obtained in triplicate; FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, and FIG. 5F illustrate the specific binding of the bivalent-IA-Cy5.5 with U-87 cells. FIG. 5A and FIG. 5D are fluorescence images, FIG. 5B and FIG. 5E are bright-field images, and FIG. 5C and FIG. 5F are fusion images, each taken from the same field-of-view. Confocal laser-scanning microscopy images of U-87 glioblastoma incubated with bivalent-IA-Cy5.5 demonstrated endocytosis of the imaging probes (FIG. 5A through FIG. 5C). A U-87 cell-blocking study using non-fluorescent bivalent IA demonstrated a complete blockage of endocytosis of the imaging probes (see FIG. 5D, FIG. 5E, and FIG. 5F); FIG. 6A and FIG. 6B show photographic, and corresponding near-infrared images, respectively, of a time-course series of a live U-87 xenograft tumor-bearing mouse, recorded at selected time points. The photon scale is shown on the right in series FIG. 6A, while the corresponding radiance scale is shown on the right for the series in FIG. 6B (p/sec/cm2/sr). The murine subject in this illustrative study was anesthetized with 1.5-2.0% isoflurane through a nosecone. The arrow in the 48-hr time-point indicates the location of the tumor within the body of the mouse; FIG. 7 shows a representative region of interest (ROI) analysis of fluorescence signal (radiance) from a tumor relative to that of normal tissue (T/N) over time (in hrs) following bivalent-IA-Cy5.5 administration. Error bars at each time point represents standard deviation from n=5 subjects; FIG. 8 shows the competitive inhibition of bivalent-IA-Cy5.5 conjugate with non-fluorescent bivalent IA. Significant blocking of tumor fluorescence signal (y-axis) was observed at all time points (x-axis). The units of radiance are in p/s/cm2/sr; error bars indicate the standard deviation from n=6 blocked, n=4 non-blocked; FIG. 9A, FIG. 9B, FIG. 9C, and FIG. 9D show an illustrative imaging study in accordance with one aspect of the present invention. FIG. 9A and FIG. 9B are photographic images of live U-87 xenograft tumor-bearing mice at 24 hours post-intravenously-administered un-conjugated Cy5.5 (FIG. 9A) vs. bivalent IA-Cy5.5 (FIG. 9B), respectively (the photon scale is shown at right). The lower panel (FIG. 9C, and FIG. 9D) show the corresponding near-infrared fluorescent imaging of the same animals, with the radiance scale shown as a color bar to the right (in units of p/sec/cm2/sr). The two mice in this representative study were anesthetized with 1.5-2.0% isoflurane through a nosecone. Black paper was used to cover the injection sites in the lateral tail veins and the location of the tumors are indicated by arrows; FIG. 10A, FIG. 10B, and FIG. 10C show representative ex vivo NIR imaging of major internal organs harvested from a xenograft tumor-bearing mice at 24 hours post i.v. injection of bivalent IA-Cy5.5. FIG. 10A (top panel) is a photographic image (photon scale shown to the right), while FIG. 10B (bottom panel) is a fluorescence image (in units of p/sec/cm2/sr) of the same organs. Harvested organs were: kidneys (k); liver (li); heart and lungs (h/l); small and large intestines (gi); spleen (sp), and the U-87 tumor (tu); FIG. 10C shows the biodistribution of bivalent IA-Cy5.5 at 24 hrs' post-injection averaged from two subjects, with the Y-axis presented in units of total photon flux per gram of tissue; FIG. 11 shows the chemical structures of exemplary compounds in accordance with one aspect of the present invention. Shown are the compounds IA (1), IAC (2) and bivalent ligands (3), (4), (5), (6), (7), and (8); FIG. 12 shows a generalized illustrative synthetic pathway for the synthesis of bivalent ligand compounds (3), (4), (5), (6), (7), and (8) in accordance with one aspect of the present invention; FIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, FIG. 13E, and FIG. 13F show illustrative examples of the binding of selected antagonists with integrin in accordance with one aspect of the present invention. In each representation, the corresponding structural conformations of the interacting antagonists are offset and enlarged to better show their molecular details. FIG. 13A: IA monomer compound (1); FIG. 13B: IA dimer compound (4) (n=2); FIG. 13C: IA dimer compound (5) (n=6); FIG. 13D: IAC monomer compound (2); FIG. 13E: IAC dimer compound (7) (n=2); and FIG. 13F: IAC
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