Fixed #14823 -- Corrected bootstrapping problems with register_serializers....

Fixed #14823 -- Corrected bootstrapping problems with register_serializers. Thanks to miker985@uw.edu for the report and draft patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15336 bcc190cf-cafb-0310-a4f2-bffc1f526a37