Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

libexec: adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

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.

No functional change intended.

Do a better job at determining the username of the login session.

When multiple users share the same UID, the old code will simply pick an
arbitrary username to attach to the utmpx entries. Make the code a bit
more accurate by first checking whether getlogin() returns a username
which corresponds to the uid of the calling process. If this fails,
simply fall back to picking an arbitrary username.

Reported by: saurik on GitHub
MFC after: 2 weeks

Minor cleanups to ulog-helper:

- Remove unneeded linking against libmd. libulog depends on this
library, but the ulog-helper tool itself does not.

- Change the comment at the top to mention utmpx instead of utmp, wtmp
and lastlog.

- Simply use user_from_uid() to translate to a username string.

- Put variable declarations together.

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.

Repair breakage to last-minute API change.

I changed ulog_log{in,out} to return a void, but forgot to change
ulog-helper as well.

Reported by: stefanf

Add a new library: libulog.

One of the things I really want to do, is to get rid of the limitations
of our current utmp(5) mechanism:

- It only allows 8 byte TTY device names.
- The hostname only allows 16 bytes of storage.

I'm not a big fan of <utmpx.h>, but I think we should at least try to
add parts of it. Unfortunately we cannot implement <utmpx.h>, because we
miss various fields, such as ut_id, ut_pid, etc. The API provided by
libulog shares some similarities with <utmpx.h>, so it shouldn't be too
hard to port these applications eventually. In most simple cases, it
should just be a matter of removing the ulog_ prefix everywhere.

As a bonus, it also implements a function called ulog_login_pseudo(),
which allows unprivileged applications to write log entries, provided
they have a valid file descriptor to a pseudo-terminal master device.

libulog will allow a smoother transition to a new file format by adding
a library interface to deal with utmp/wtmp/lastlog files. I initially
thought about adding the functionality to libutil, but because I'm not
planning on keeping this library around forever, we'd better keep it
separated.

Next items on the todo list:

1. Port applications in the base system (and ports) to libulog, instead
of letting them use <utmp.h>.
2. Remove <utmp.h>, implement <utmpx.h> and reimplement this library on
top.
3. Port as many applications as possible back to <utmpx.h>.