Fixed #7904: added support for a "use_for_related_fields" property on managers. If True, the manager will be used for related object lookups instead of the "bare" QuerySet introduced bu [8107]. Patch from Justin Bronn.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8212 bcc190cf-cafb-0310-a4f2-bffc1f526a37