Patch 55 is also needed to get demo.py to start up from scratch.  I have
a few more patches for issues showing up with demo.py processing
requests that I still need to run the testsuite on with Python 2 before
uploading.

55. Python 3 preparation: use bytes more in password handling.

This patch adds enough fixes to use bytes to work for PBKDF2 passwords,
but probably not for the other hash algorithms supported.

It would make sense for the PBKDF2 code to use the Python hashlib
support for PBKDF2 as the first choice before M2Crypto and the local
PBKDF2 implementation (hashlib supports it in 2.7.8, 3.4 and later), but
it still seems appropriate to fix the local code to handle bytes
properly anyway.  I don't know if we'll end up supporting Python 3.3
(the minimum plausible Python 3 version, but now EOL) in Roundup or not.