Summary:
Core mercurial has a much better "nocheck" option now that we should just start
using. It's better and it's built-in!
Test Plan: Updated tests
Reviewers: #fbhgext, quark
Reviewed By: #fbhgext, quark
Subscribers: quark
Differential Revision: https://phab.mercurial-scm.org/D164
Summary: The --merge flag is relatively new; we shouldn't add --check if it is specified.
Test Plan: Unit test
Reviewers: #mercurial, quark
Reviewed By: quark
Subscribers: mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D4916396
Tasks: 17490374
Signature: t1:4916396:1492647440:d9955931cb9177719a58325c08a715d4d51d1226