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

Build usr.bin/ with WARNS=6 by default.

Also add some missing $FreeBSD$ to keep svn happy.

Add revoke(1).

While hacking on TTY code, I often miss a small utility to revoke my own
(pseudo-)terminals. This small utility is just a small wrapper around
the revoke(2) call, so you can destroy your very own login sessions.

Approved by: re