Summary:
This is an MVP to give the user more information about the state of the repo. We'll grow the functionality in other diffs.
for example, if the repo is in a state after a stalled graft, then hg status outputs a bit more
$ hg status
M a
? a.orig
# The repository is in an unfinished graft state.
Test Plan: See the tests.
Reviewers: #sourcecontrol, durham, rmcelroy
Subscribers: akushner, rmcelroy
Differential Revision: https://phabricator.fb.com/D2495659
Tasks: 8563305
