Integers coerced to float on Series construction from dictionary.
When constructing a Series from a dictionary, if the dictionary contains floats, all integer values in the dictionary are coerced to `float` **unless** the dictionary contains an integer value > `sys.maxint`.

Minimal repro case:

```
import pandas as pd
import sys

if __name__ == '__main__':

    pd.show_versions()

    # Works as expected.                                                                                                                                                                                    
    t0 = {'A': 1,
          'B': 10}

    # B gets coerced to float.                                                                                                                                                                              
    t1 = {'A': 1.5,
          'B': 10}

    # B gets coerced to float.                                                                                                                                                                              
    t2 = {'A': 1.5,
          'B': 10,
          'C': sys.maxint}

    # B is not coerced if the dictionary contains a value > maxint.                                                                                                                                         
    t3 = {'A': 1.5,
          'B': 10,
          'C': sys.maxint + 1}

    test_0 = pd.Series(t0)
    test_1 = pd.Series(t1)
    test_2 = pd.Series(t2)
    test_3 = pd.Series(t3)

    for test in test_0, test_1, test_2, test_3:
        print "Type at index B is %s" % format(type(test.B))
```

Output:

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Darwin
OS-release: 13.1.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.14.1
nose: 1.3.3
Cython: 0.20.1
numpy: 1.8.1
scipy: 0.13.2
statsmodels: 0.5.0
IPython: 2.2.0
sphinx: 1.2.1
patsy: 0.2.1
scikits.timeseries: None
dateutil: 2.2
pytz: 2014.4
bottleneck: None
tables: 3.1.1
numexpr: 2.4
matplotlib: 1.3.1
openpyxl: None
xlrd: 0.9.3
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: 0.8
apiclient: None
rpy2: None
sqlalchemy: None
pymysql: None
psycopg2: None

Type at index B is <type 'numpy.int64'>
Type at index B is <type 'numpy.float64'>
Type at index B is <type 'numpy.float64'>
Type at index B is <type 'int'>
```

Stepping through the code, the coercion looks like it's happening in the call to `lib.fast_multiget` at https://github.com/pydata/pandas/blob/v0.14.1/pandas/core/series.py#L191.
