Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

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.

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>.