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