void dock_undock_objects(object *objp1, object *objp2)
{
	Assert(objp1 != NULL);
	Assert(objp2 != NULL);

	// remove objects from each others' dock lists
	dock_remove_instance(objp1, objp2);
	dock_remove_instance(objp2, objp1);
}
void dock_undock_objects(object *objp1, object *objp2)
{
#ifndef NDEBUG
	if ((dock_find_instance(objp1, objp2) == NULL) || (dock_find_instance(objp2, objp1) == NULL))
	{
		Error(LOCATION, "Trying to undock an object that isn't docked!\n");
	}
#endif

	// remove objects from each others' dock lists
	dock_remove_instance(objp1, objp2);
	dock_remove_instance(objp2, objp1);
}