title: Objects with permissions assigned by django-guardian not visible in admin
body: <p>I'm using <a href="https://github.com/lukaszb/django-guardian" rel="noreferrer">django-guardian</a> in order to manage per object permission.</p>
  
  <p>For a given user I give permission all permission on one object:</p>
  
  <pre><code>joe = User.objects.get(username="joe")
  
  mytask = Task.objects.get(pk=1)
  
  assign('add_task', joe, mytask)
  assign('change_task', joe, mytask)
  assign('delete_task', joe, mytask)
  </code></pre>
  
  <p>and I get, as expected:</p>
  
  <pre><code>In [57]: joe.has_perm("add_task", mytask)
  Out[57]: True
  
  In [58]: joe.has_perm("change_task", mytask)
  Out[58]: True
  
  In [59]: joe.has_perm("delete_task", mytask)
  Out[59]: True
  </code></pre>
  
  <p>In admin.py I also make TaskAdmin inherit from <code>GuardedModelAdmin</code> instead of <code>admin.ModelAdmin</code></p>
  
  <p>Now when I connect to my site with joe, on the admin I get:</p>
  
  <pre><code>You don't have permission to edit anything 
  </code></pre>
  
  <p>Am I not supposed to be able to edit the object mytask?</p>
  
  <p>Do I have to set some permissions using the built-in model-based permission system?</p>
  
  <p>Am I missing anything?</p>
  
  <p><b>EDIT</b></p>
  
  <p>I tried to add the option <code>user_can_access_owned_objects_only</code>, which is supposed to deal with my issue, but I still can't see anything in my admin...</p>
  
  <pre><code>class TaskAdmin(GuardedModelAdmin):
  
      user_can_access_owned_objects_only = True
  
      pass
  
  admin.site.register(Task, TaskAdmin)
  </code></pre>
  
  <p>Thank you</p>