utmpx.h: fix comment missed in r. 1.10 _NETBSD_SOURCE changes

don't do size computations because g++ does not like it.

merge christos-time_t

branches: 1.15.10;
Remove clause 3 and 4 from TNF licenses

branches: 1.14.16;
Add run level messages.

compat code reorg

de-__P -- the hack is long since useless. Discussed with christos,
matt, kleink, others. Approved by christos.

Make getlastlogx have the pathname to the lastlogx database as first
argument, to be consistent with updlastlogx.

Approved by christos, reviewed by kleink.

[The lastlogxname function should not be used any longer.]

Add a new feature-test macro, _NETBSD_SOURCE. If this is defined
by the application, all NetBSD interfaces are made visible, even
if some other feature-test macro (like _POSIX_C_SOURCE) is defined.
<sys/featuretest.h> defined _NETBSD_SOURCE if none of _ANSI_SOURCE,
_POSIX_C_SOURCE and _XOPEN_SOURCE is defined, so as to preserve
existing behaviour.

This has two major advantages:
+ Programs that require non-POSIX facilities but define _POSIX_C_SOURCE
can trivially be overruled by putting -D_NETBSD_SOURCE in their CFLAGS.
+ It makes most of the #ifs simpler, in that they're all now ORs of the
various macros, rather than having checks for (!defined(_ANSI_SOURCE) ||
!defined(_POSIX_C_SOURCE) || !defined(_XOPEN_SOURCE)) all over the place.

I've tried not to change the semantics of the headers in any case where
_NETBSD_SOURCE wasn't defined, but there were some places where the
current semantics were clearly mad, and retaining them was harder than
correcting them. In particular, I've mostly normalised things so that
_ANSI_SOURCE gets you the smallest set of stuff, then _POSIX_C_SOURCE,
_XOPEN_SOURCE and _NETBSD_SOURCE in that order.

Tested by building for vax, encouraged by thorpej, and uncontested in
tech-userlevel for a week.

Add __P(()); noticed by wiz.

updates to lastlogx implementation.

forward declaration for struct utmp.

- reverse the #define ut_user<->ut_name so that we don't affect utmp.
- add a couple of gnuisms.

branches: 1.5.2;
add a couple of XOPEN compatibility defines, and a non-xopen function that
we are expected to have (updwtmpx). Requested by tron.

Include "sys/time.h" here to get the definition of "struct timeval".

s/ut_name/ut_user/ from Simon Burge.

- include <sys/socket.h> because we use sockaddr_storage
- it is PATH_LASTLOGX not PATH_LASTLOG

A utmpx implementation.