Fixed #16918 -- Ensured that custom querysets are used when provided to...

Fixed #16918 -- Ensured that custom querysets are used when provided to `BaseDateDetailView.get_object()`. Thanks to mitar for the report, to koenb for the patch and to Preston Holmes for the review.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16974 bcc190cf-cafb-0310-a4f2-bffc1f526a37