Log Message:
devel/py-hg-cinnabarclone: Import hg extension from git-cinnabar.

This simple server-side hg extension can advertise bundles to speed
up `git clone' with git-cinnabar.

Single Python file distributed as part of git-cinnabar -- need not
pull in all of git-cinnabar (and Rust) on the server to run.

Not 100% sure if this use of PY_COMPILE_ALL/PY_COMPILE_O_ALL is
appropriate -- review and/or tweaks welcome.