title: 500-error when adding a picture
body: <p>In Django-CMS, I select the picture plugin and add a picture from my harddrive, then when I click on that picture-plugin I get the error as seen below. What is the reason for this? </p>
  
  <pre><code>    ValueError at /admin/cms/page/2/edit-plugin/7/cms_page_media/2/parking_mockup.png/
  invalid literal for int() with base 10: '2/edit-plugin/7/cms_page_media/2/parking_mockup.png'
  Request Method: GET
  Request URL:    http://localhost:8000/admin/cms/page/2/edit-plugin/7/cms_page_media/2/parking_mockup.png/
  Django Version: 1.3.1
  Exception Type: ValueError
  Exception Value:    
  invalid literal for int() with base 10: '2/edit-plugin/7/cms_page_media/2/parking_mockup.png'
  Exception Location: C:\Python27\lib\site-packages\django\db\models\fields\__init__.py in get_prep_value, line 479
  Python Executable:  C:\Python27\python.exe
  Python Version: 2.7.2
  Python Path:    
  ['C:\\djangoworkspace\\hulawai',
   'C:\\Python27\\lib\\site-packages\\django_classy_tags-0.3.4.1-py2.7.egg',
   'C:\\Python27\\lib\\site-packages\\django_sekizai-0.5-py2.7.egg',
   'C:\\Python27\\lib\\site-packages\\html5lib-0.95-py2.7.egg',
   'C:\\Python27\\lib\\site-packages\\virtualenv-1.7.1.2-py2.7.egg',
   'C:\\Python27\\lib\\site-packages\\pip-1.1-py2.7.egg',
   'C:\\Windows\\system32\\python27.zip',
   'C:\\Python27\\DLLs',
   'C:\\Python27\\lib',
   'C:\\Python27\\lib\\plat-win',
   'C:\\Python27\\lib\\lib-tk',
   'C:\\Python27',
   'C:\\Python27\\lib\\site-packages',
   'C:\\Python27\\lib\\site-packages\\PIL']
  Server time:    Thu, 22 Mar 2012 11:03:58 +0100
  Traceback Switch to copy-and-paste view
  
  C:\Python27\lib\site-packages\django\core\handlers\base.py in get_response
                      for middleware_method in self._view_middleware:
                          response = middleware_method(request, callback, callback_args, callback_kwargs)
                          if response:
                              break
                  if response is None:
                      try:
                          response = callback(request, *callback_args, **callback_kwargs) ...
                      except Exception, e:
                          # If the view raised an exception, run it through exception
                          # middleware, and if the exception middleware returns a
                          # response, use that. Otherwise, reraise the exception.
                          for middleware_method in self._exception_middleware:
                              response = middleware_method(request, e)
  </code></pre>
  
  <p><strong>UPDATE</strong> Full stacktrace available here: <a href="https://gist.github.com/2157837" rel="nofollow">https://gist.github.com/2157837</a></p>