backend.

This allows Querysets to be cached for Oracle and should provide a model for
adding pickling support to other (external) database backends that need a
custom Query class.

Thanks to Justin Bronn for some assistance with this patch.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@9272 bcc190cf-cafb-0310-a4f2-bffc1f526a37