title: has no attribute '_meta' error when creating a ModelAdmin object
body: <p>I am new to Django and I was trying to customize the Admin interface for my model but I get an error when trying to add a ModelAdmin object. My code and error is included below. If i take out the BlogAdmin object from the register statement, I don't get any errors and the site loads fine.</p>
  
  <p>Thanks for your help!</p>
  
  <pre><code>class Blog(models.Model):
      name = models.CharField(max_length=300)
      url = models.URLField()
  
  class BlogAdmin(admin.ModelAdmin):
      list_display = ['name', 'url']
      search_fields = ["name"]
  
  admin.site.register([Blog,BlogAdmin])
  </code></pre>
  
  <p>I get the following error:</p>
  
  <p>type object 'BlogAdmin' has no attribute '_meta'</p>
  
  <pre><code>Exception Location:     /Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/django/contrib/admin/sites.py in register, line 80
  Python Executable:  /Users/Bilal/Development/Django/ENV/traveller3/bin/python
  Python Version:     2.7.1
  Python Path:    
  
  ['',
   '/Applications/PyCharm.app/helpers/pydev',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/pip-1.0.2-py2.7.egg',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/MySQL_python-1.2.3c1-py2.7-macosx-10.7-intel.egg',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/scikit_learn-0.9-py2.7-macosx-10.7-intel.egg',
   '/Users/Bilal/Development',
   '/Library/Python/2.7/site-packages/pip-1.0.2-py2.7.egg',
   '/Users/Bilal/Development/scrapyard',
   '/Applications/PyCharm.app/helpers',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python27.zip',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/plat-darwin',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/plat-mac',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/plat-mac/lib-scriptpackages',
   '/Users/Bilal/Development/Django/ENV/traveller3/Extras/lib/python',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/lib-tk',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/lib-old',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/lib-dynload',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/PIL',
   '/Library/Python/2.7/site-packages',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/PyObjC',
   '/Users/Bilal/Development/Django/ENV/traveller3/lib/python2.7/site-packages/IPython/extensions']
  </code></pre>