[1.2.X] Fixed #11319 - Added lookup support for ForeignKey.to_field. Also...

[1.2.X] Fixed #11319 - Added lookup support for ForeignKey.to_field. Also reverted no-longer-needed model formsets workaround for lack of such support from r10756. Thanks Russell and Alex for review.

Backport of r15303 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15304 bcc190cf-cafb-0310-a4f2-bffc1f526a37