[1.1.X] Fixed #12121 -- Modified __reduce__ on a model to avoid an infinite...

[1.1.X] Fixed #12121 -- Modified __reduce__ on a model to avoid an infinite recursion problem that occurs on Python 2.4. Thanks to emulbreh for the report.

Backport of r11691 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@11692 bcc190cf-cafb-0310-a4f2-bffc1f526a37