[1.1.X] Fixed #12876 -- Corrected a problem with recursive relations under...

[1.1.X] Fixed #12876 -- Corrected a problem with recursive relations under deepcopy. Thanks to elachuni for the patch.

Backport of r12700 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12702 bcc190cf-cafb-0310-a4f2-bffc1f526a37