Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Somehow this got replicated too many times

Approved by: cperciva (implicit)

Add a clean-room reimplementation of a script originally
found in openssh's contrib directory.

This version has more features and is better written.
I intend to submit this upstream as well.

Reviewed by: bapt
Reviewed by: des
Approved by: cperciva
MFC after: 1 week