Fixed #3400 -- Support for lookup separator with list_filter admin option....

Fixed #3400 -- Support for lookup separator with list_filter admin option. Thanks to DrMeers and vitek_pliska for the patch!

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14674 bcc190cf-cafb-0310-a4f2-bffc1f526a37