Merge from CheriBSD:
commit 1b41f6de7ca09e04fdc6f66bc478ea6c981a41b9
Author: Brooks Davis <brooks@one-eyed-alien.net>
Date: Mon Jan 27 22:59:02 2014 +0000

Now that mtree is always nmtree use it as mtree

Tested on: ref9-amd64
X-MFC after: never
Sponsored by: DARPA, AFRL