Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

zdiff: avoid non-conformant features

`setvar` is a non-conformant feature that looks slightly neater but is
not portable to other /bin/sh implementations. Making the script
portable is straightforward, so let's do it.

Tests are added to make sure that I didn't break anything major in the
process.

Reviewed by: bapt (previous version), jilles
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D35275

Diff reduction against NetBSD. The most notable change is to zdiff(1) to
handle more file formats including bzip2 and xz.

MFC after: 2 weeks

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.

Replace the GNU gzip with a slightly modified NetBSD gzip. The
NetBSD version is a feature-to-feature re-implementation of GNU
gzip using the freely-redistributable zlib and this version is
expected to be mostly bug-to-bug compatible with the GNU
implementation.

- Because this is a piece of mature code and we want to make
changes so it is added directly rather than importing to
src/contrib.
- Connect newly added code to src/usr.bin/ and rescue/rescue
build.
- Disconnect the GNU gzip code from build for now, they will
be eventually removed completely.
- Provide two new src.conf(5) knobs, WITHOUT_BZIP2_SUPPORT and
WITHOUT_BZIP2.

Tested by: kris (full exp-7 pointyhat build)
Approved by: core (importing a 4-clause BSD licensed file)
Approved by: re (adding new utility during -HEAD code slush)