self-referential and circular relations. A lot of community debugging went into
this fix, so thanks to bmurdock@gmail.com, Marek Kubica, ramiro, Michael
Radziej (the last two giving test cases showing the problem) and James Bennett
(who did the hard work to actually diagnose the true problem and fix it).
git-svn-id: http://code.djangoproject.com/svn/django/trunk@4676 bcc190cf-cafb-0310-a4f2-bffc1f526a37