Fixed #15221 -- Made the admin filters on foreign key and m2m relationships...

Fixed #15221 -- Made the admin filters on foreign key and m2m relationships display the related field's verbose name instead of that of the related model.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16991 bcc190cf-cafb-0310-a4f2-bffc1f526a37