Merge from CheriBSD:
commit 6b569451b92c48ccf1768da32e7e89189e1aa253
Author: Brooks Davis <brooks@one-eyed-alien.net>
Date:   Mon Jan 27 22:50:46 2014 +0000

    Always install nmtree as mtree.
    For compability, link mtree to nmtree.

X-MFC after:	never
Sponsored by:	DARPA, AFRL
Merge from CheriBSD:
commit 70b8f0c127db6b80411789d237b403cc64a93573
Author: Brooks Davis <brooks@one-eyed-alien.net>
Date:   Mon Jan 27 22:53:57 2014 +0000

    Move mtree.5 to usr.sbin/nmtree.
    Remove note that mtree 2.0 format files aren't supported.

MFC after:	4 weeks
Sponsored by:	DARPA, AFRL
Merge from CheriBSD:
commit 2d581e8caf79d7a0f5a24590eccd06da90cccb74
Author: Brooks Davis <brooks@one-eyed-alien.net>
Date:   Mon Jan 27 22:57:51 2014 +0000

    Add WITHOUT_FMTREE to disable building fmtree.

MFC after:	4 weeks
Sponsored by:	DARPA, AFRL
Add file missed in r261296.

MFC after:	4 weeks
Sponsored by:	DARPA, AFRL