MFC r314653:

libexec: normalize paths using SRCTOP-relative paths or :H when possible

This simplifies make logic/output

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

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

Make WARNS=6 the default for libexec/.

Just like bin/ and sbin/, I think setting WARNS to the highest value
possible will make it more attractive for people to fix warnings.

- The WARNS variable is set in the Makefile in the directory of the
application itself, making it more likely that it will be removed out
of curiosity to see what happens.
- New applications will most likely build with WARNS=6 out of the box,
because the author would more likely fix the warnings during
development than lower WARNS.

Unfortunately almost all apps in libexec require a lowered value of
WARNS.

Fixed static linkage (build with -DNO_SHARED).

Approved by: re (kensmith)

Add PAM support to atrun(8).

Use a single setusercontext(3) instead of a bunch of basic syscalls.
Besides aesthetic benefits, that makes at(1) jobs subject to such
login.conf(5) settings as resource limits.

Lock down with WFORMAT?=1, with overrides in the subdirectories which
are not yet warning-clean. Tested on i386 and alpha.

- Backout botched attempt to intoduce MANSECT feature.
- MAN[1-9] -> MAN.

Don't use MANDEPEND and MANSRC.

Set the default manual section for libexec/ to 8.

Don't uselessly set MANDEPEND (it isn't used in this Makefile, and isn't
really used in bsd.man.mk).

Don't uselessly set MANSRC ("." is in the path by default, and there are
no ordering problems).

Fixed some other style bugs.

$Id$ -> $FreeBSD$

Revert $FreeBSD$ to $Id$

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.

Fix ${.CURDIR} misspelling

Upgrade to 2.9

Upgrade.
Close security holes reported.

Added the Linux atrun command as hacked by Chris Demetriou for NetBSD.