Fixed #9969: choices with options groups (added in [7977]) now work correctly...

Fixed #9969: choices with options groups (added in [7977]) now work correctly in the admin with list_display and list_filter. Thanks, ramiro.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10318 bcc190cf-cafb-0310-a4f2-bffc1f526a37