I realized that there is a nasty interaction between the trashcan and __del__: if you're very close to the trashcan limit and you're calling __del__, then objects that should have been deallocated in __del__ (in particular, an object involving self) might instead end up in the trashcan. So self might be resurrected when it shouldn't be.

This is causing test failures in the 2.7 backport due to a different implementation of __del__.