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

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

nos-tun(8): make WARNS=3 clean

The renames are in spirit of DragonflyBSD, to keep diff minimal.

PR: bin/140060
Approved by: ed (co-mentor)

style.Makefile(5):
Use WARNS?= instead of WARNS=.

Default to WARNS=2.
Binary builds that cannot handle this must explicitly set WARNS=0.

Reviewed by: mike

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

Set the default manual section for sbin/ to 8.

Program which implements "nos" alias "ka9q" alias "IP-IP" tunnels.

PR: 1154
Reviewed by: phk
Manpage by: phk
Submitted by: Nickolay N. Dudorov nnd@itfs.nsk.su