Breezy is the most recent of the two, and works on Python 3 while being
compatible with the (old) Bazaar file format.

This patch contains a variety of unicode <-> bytes changes, API breakage fixing,
restoring failing imports and changing the executable from `bzr` to `brz`.

I recommend using the debian packages for `brz` and `python3-breezy` (3.1+),
because the pip package seems to be haunted by radioactive dragons.

Differential Revision: https://phab.mercurial-scm.org/D10513