Fixed #16481 -- Adapted one raw SQL query in cull immplementation of the...

Fixed #16481 -- Adapted one raw SQL query in cull immplementation of the database-based cache backend so it works with Oracle. Thanks Aymeric Augustin for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16635 bcc190cf-cafb-0310-a4f2-bffc1f526a37