title: tastypie api not showing ForeignKey in json result
body: <p>I recently started using tastypie to open up my api for a potential smartphone app.</p>
  
  <p><strong>I'm using python-2.7 and Django-1.1.2</strong></p>
  
  <p>Two things are confusing me</p>
  
  <p>1: in the <code>EntryResource</code> class when calling the <code>ForeignKey</code>, they just call the resource along with the resource_name, when I do it in such a way I get the following traceback.</p>
  
  <pre><code>691. assert isinstance(to, basestring), "%s(%r) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string %r" % (self.__class__.__name__, to, RECURSIVE_RELATIONSHIP_CONSTANT)
  
  Exception Type: AssertionError at /api/v1/activity-stream-item-subject/
  Exception Value: ForeignKey(&lt;class 'api.resources.UserResource'&gt;) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string 'self'
  </code></pre>
  
  <p>2: if I change <code>EntryResource</code> to <code>user = fields.ForeignKey(UserResource, 'user')</code>, then it runs fine without a traceback, however I cannot see the related information in the JSON response.</p>
  
  <p>api/resources.py</p>
  
  <pre><code>class UserResource(ModelResource):
      class Meta:
          queryset = User.objects.all()
          resource_name = 'user'
          excludes = ['email', 'password', 'is_active', 'is_staff', 'is_superuser']
          filtering = {
              'username': ALL,
          }
  
  class EntryResource(ModelResource):
      user = fields.ForeignKey(UserResource, 'user')
  
      class Meta:
          queryset = Entry.objects.all()
          resource_name = 'entry'
          authorization = Authorization()
          filtering = {
              'user': ALL_WITH_RELATIONS,
              'pub_date': ['exact', 'lt', 'lte', 'gte', 'gt'],
          } 
  </code></pre>
  
  <p>Any ideas?</p>