- Made cls.__module__ writable.

- Ensure that obj.__dict__ is returned as {}, not None, even upon first
  reference; it simply springs into life when you ask for it.

(*) The pickling support is provisional for the following reasons:

- It doesn't support classes with __slots__.

- It relies on additional support in copy_reg.py: the C method
  __reduce__, defined in the object class, really calls calling
  copy_reg._reduce(obj).  Eventually the Python code in copy_reg.py
  needs to be migrated to C, but I'd like to experiment with the
  Python implementation first.  The _reduce() code also relies on an
  additional helper function, _reconstructor(), defined in
  copy_reg.py; this should also be reimplemented in C.