mq: update the dirstate and its parent within a `parentchange` context

This is more correct, and move our plan of separated API for different dirstate
usage forward.

note: maybe the `parentchange` context manager should replace the dirstateguard
entirely ? (in this case we should probably deprecated dirstateguard).

Differential Revision: https://phab.mercurial-scm.org/D11017

hgext/mq.py

@@ -2002,6 +2002,8 b' class queue(object):'
 
             bmlist = repo[top].bookmarks()
 
+            with repo.dirstate.parentchange():
+                # XXX do we actually need the dirstateguard
             dsguard = None
             try:
                 dsguard = dirstateguard.dirstateguard(repo, b'mq.refresh')