Fixed #13003 -- Ensured that ._state.db is set correctly for select_related()...

Fixed #13003 -- Ensured that ._state.db is set correctly for select_related() queries. Thanks to Alex Gaynor for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12701 bcc190cf-cafb-0310-a4f2-bffc1f526a37