- Need to handle exception instances embedded within others.

  I dealt with this in msgpack using a "default" option (essentially a
  msgpack/json form of reduce).

  For pickle, we're still creating instance pickles in this case. :/

- Use a python-msgpack option to produce tuples rather than
  lists.  The ZEO protocol uses tuples far more often than lists.

  This really mostly or entirely affects tests.

  Removed workarounds for some test code that expected tuples and
  added some for test code that expects lists. :)