Could the PyObject_ClearWeakRefs(self); call in the middle of the lines 
del_changes_class.patch adds also be used to cause python code to set 
__del__ or __dict__ causing the wrong destructor or wrong dict to be 
DECREFed?

(I'm trying to wrap my head around the possibilities here and come up 
with a test case of that but weakref isn't behaving as i'd expect)