'Makes a copy of the manager and assigns it to \'model\', which should be
a child of the existing model (used when inheriting a manager from an
abstract base class).'

def _copy_to_model(self, model):

    assert issubclass(model, self.model)
    mgr = copy.copy(self)
    mgr._set_creation_counter()
    mgr.model = model
    mgr._inherited = True
    return mgr
