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.

Fixed the only warning and mark as WARNS=6 clean.

Add C rewrites of catman and makewhatis. These aren't quite as
the submitter supplied them, as I did some WARNS=n fixups (mostly
const-ification).

Submitted by: John Rochester <john@jrochester.org>