Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: initial adoption of licensing ID tags.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Initially, only tag files that use BSD 4-Clause "Original" license.

RelNotes: yes
Differential Revision: https://reviews.freebsd.org/D13133

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

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.

o __P removal
o register removal
o use new style prototypes and function definitions

$Id$ -> $FreeBSD$

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.

Close PR #2193: support backslash line continuations.
(Also did some minor cleanups.)

Small touchups:

- Fix typos in comments in hash.c.
- Remove unneeded and unused member from grouplist struct in hash.h.
(Curiously, the compiler never complained about this even though the
member was of type 'struct grps' which is not defined anywhere in
this program.)
- char ch -> int ch in revnetgroup.c.
- char *argv[0]; -> char *argv[]; also in revnetgroup.c.
- Force the user to specify at least one of the -u or -h flags
and complain if they specify both.

Import the first cut of my (finally finished) revnetgroup program. This
program parses the /etc/netgroup file into netgroup.byuser and netgroup.byhost
format for NIS.

I used hash tables to store the initial netgroup data in memory and to
construct the 'reverse' netgroup output. It seems just as fast as the
SunOS revnetgroup, which is surprising considering this is my first
attempt at using hash tables in a real application. :)

Note that I canibalized a large chunk of getnetgrent.c to save myself
from having to write my own netgroup parsing functions.