Fix two instances of undefined behaviour in contrib/nvi.

Found by: clang ToT
Obtained from: NetBSD
Reviewed by: jh
MFC after: 3 days

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Fixes from NetBSD for nvi visual mode:

- Fix handling of ^@ when reading an ex command. Don't try to replay
the previous input.
- Fix handling of ^C in insert mode and when reading an ex command.
Repeating an interrupted input could cause a crash and interrupting
ex command input could cause a file corruption.
- Fix a bug which causes crashes in file name completion when a file
name is longer than the screen width.
- When an error occurs in v_txt(), leave the input mode.

PR: bin/21089, bin/136393
Obtained from: NetBSD

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

Import of nvi-1.79, minus a few bits that we dont need (eg: postscript
files, curses, db, regex etc that we already have). The other glue will
follow shortly.

Obtained from: Keith Bostic <bostic@bostic.com>