This is pretty messy. :(  Ideally we would disallow setting sys.modules to anything except a dict (or perhaps any mapping).  However, we don't have that option currently (see https://github.com/ericsnowcurrently/cpython/tree/sys-module).  In the meantime we have to fix up all the places that are expecting a mapping.

Part of the problem here is that a number of places fail silently, as evidenced by the failures Oren pointed out...