Fixed #7270 -- Added the ability to follow reverse OneToOneFields in select_related(). Thanks to George Vilches, Ben Davis, and Alex Gaynor for their work on various stages of this patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12307 bcc190cf-cafb-0310-a4f2-bffc1f526a37