Move some of the test framework code from .py to .txt, and add a more
detailed comment at the top about the contract between .txt and the
.py file that uses it.

Move the interface test into .txt.  I guess it's not so bad.

Change some tests that displayed the contents of __dict__.  Other
persistent implementations may have extra state in __dict__.

Remove B, it is unused.

Change DocFileSuite() to accept an explicit set of globals.

Remove the pickling/P2 test, because it was too hard to make work with
the framework.  Include comment explaining how such a test should be
added.