Fixed #11286 -- Ensured that dumpdata uses the default manager, rather than...

Fixed #11286 -- Ensured that dumpdata uses the default manager, rather than always using the manager called `objects`. Thanks to Marc Remolt for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10967 bcc190cf-cafb-0310-a4f2-bffc1f526a37