Fixed #7448 -- Convert "in" filters to pass in the correct values for datetimes

and similar complex objects.

Based on patches from cgrady and alexkosholev. Refs #7707.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7883 bcc190cf-cafb-0310-a4f2-bffc1f526a37