Fixed #11120 -- Corrected handling of inlines attached to inherited classes,...

Fixed #11120 -- Corrected handling of inlines attached to inherited classes, broken by r10756. Thanks to George Song and Michael Strickland for the simultaneous reports.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10787 bcc190cf-cafb-0310-a4f2-bffc1f526a37