tests/test-parseindex2.py.out

phases: introduce phasecache

The original motivation was changectx.phase() had special logic to
correctly lookup in repo._phaserev, including invalidating it when
necessary. And at other places, repo._phaserev was accessed directly.

This led to the discovery that phases state including _phaseroots,
_phaserev and _dirtyphase was manipulated in localrepository.py,
phases.py, repair.py, etc. phasecache helps encapsulating that.

This patch replaces all phase state in localrepo with phasecache and
adjust related code except for advance/retractboundary() in phases.
These still access to phasecache internals directly. This will be
addressed in a followup.

done