Fixed #6641 -- If we lose a race when creating a new object in get_or_create,

re-get the result from the database and return that. Thanks, Jeff Guinness and
Timothée Peignier.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7289 bcc190cf-cafb-0310-a4f2-bffc1f526a37