Two more refinements of the cleanup process. (1) Explicitly clear __builtin__._ and sys.{last,exc}_* before clearing anything else. These are common places where user values hide and people complain when their destructors fail. Since the modules containing them are deleted *last* of all, they would come too late in the normal destruction order. Sigh. (2) Add some debugging aid to cleanup (after a suggestion by Marc Lemburg) -- print the names of the modules being cleaned, and (when -vv is used) print the names of the variables being cleared.