largely due to:

* Different pickle size in Python
  (even for protocol 1, where new padding is added as far as I can tell.)

* Weak references do not seem to work correctly.

* When all tests are run, committing transactions fails. Probably some
  tests are not cleaning up enough after themselves.

The biggest issue remaining at this point is the fork of Python 3.3's
pickle to properly load Python 2 binary strings and adding back
``noload()`` to the unpickler.