title: Filter haystack result with SearchQuerySet
body: <p>I'm using haystack with whoosh, trying to restrict search results to entries created by the currently logged in user only.
  The category model, for which I created an index, has a foreign key:</p>
  
  <pre><code>user = models.ForeignKey(User, editable=False)
  </code></pre>
  
  <p>And in my custom search view I want to filter like this:</p>
  
  <pre><code>searchqueryset = SearchQuerySet().filter(user=request.user.id)
  
  form = SearchForm(request.GET, searchqueryset=searchqueryset, load_all=True)
  
      if form.is_valid():
          query = form.cleaned_data['q']
          results = form.search()
  </code></pre>
  
  <p>In the database there is one entry for table category:</p>
  
  <pre><code>id  name    user_id 
  1   test10  1   
  </code></pre>
  
  <p>And the current user id is indeed 1.
  But I get No results.</p>
  
  <p>When I do this:</p>
  
  <pre><code>searchqueryset = None
  </code></pre>
  
  <p>I get the "test10" category entry.
  So does anyone know why the user id filter isn't working as expected?</p>