convert/mtn: convert suspended branches as closed branches Monotone treats branch closing ("suspending") in a similar manner to how we do in mercurial - a cert is added to a revision that marks the branch to be hidden. If a subsequent commit is made, the branch is effectively reopened.

rebase: don't mark file as removed if missing in parent's manifest (issue2725)

windows: use win32.unlink in unlinkpath() os.unlink fails to remove files with READONLY attribute