Support Django entity cloning method

[wojtekzozlak]

Django supports comfortable way to clone ORM entites by assigning None to a primary key field and calling a 'save()' method. For example:

x = Entity.objects.get(id=1) x.id 1 x.id = None x.save() x.id 3L

But polymorphic model is just regaining its id, and no new entites are created.