Thanks to Martin v. Loewis for having done some of the initial lifting
for a DZUG talk. I used a lot of his changes from this diff:

http://www.dcl.hpi.uni-potsdam.de/home/loewis/zodb/ZODB.diff

Applied all changes manually to make sure I do understand them and that
they are correct.

As always 90% of the work is to catch all places where we want to deal
with bytes instead of strings.