New rules for deleting modules. Rather than having an elaborate scheme based on object's types, have a simple two-phase scheme based on object's *names*: /* To make the execution order of destructors for global objects a bit more predictable, we first zap all objects whose name starts with a single underscore, before we clear the entire dictionary. We zap them by replacing them with None, rather than deleting them from the dictionary, to avoid rehashing the dictionary (to some extent). */