Fixed #12252 -- Ensure that queryset unions are commutative. Thanks to...

Fixed #12252 -- Ensure that queryset unions are commutative. Thanks to benreynwar for the report, and draft patch, and to Karen and Ramiro for the review eyeballs and patch updates.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15726 bcc190cf-cafb-0310-a4f2-bffc1f526a37