fix NoReverseMatch exception with Django 1.7b2

The object history view in Django 1.7b2 crashed with a `NoReverseMach`  exception:
`Reverse for 'app_list' with arguments '()' and keyword arguments '{u'app_label': ''}' not found.`
I guess this is due to:
https://github.com/django/django/commit/ba60fcbcf7645afd82f3135ecb56562f8a9c9824