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.

o style: WARNS= -> WARNS?=.

Spotted by: ru

o By popular demand import getent(1) utility: a program retrieves
and displays entries from the administrative database specified by
database, using the lookup order specified in nsswitch.conf(5).

PR: bin/79903, bin/88460, bin/96536
Submitted by: Julien Gabel, Dan Nelson, Daniel J. O'Connor
Obtained from: NetBSD
Discussed with: ume, soc-bushman
MFC after: 1 month