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)

Mechanically kill hard sentence breaks and double whitespaces.

Mdoc Janitor:

* Fix hard sentence breaks.

mdoc(7) police: Use the new .In macro for #include statements.

More at_shutdown(9) removal.

at_shutdown(9) hasn't existed since revision 1.61 of kern_shutdown.c.

mdoc(7) police: remove extraneous .Pp before and/or after .Sh.

$Id$ -> $FreeBSD$

Add $Id$, to make it simpler for members of the translation teams to
track.

The $Id$ line is normally at the bottom of the main comment block in the
man page, separated from the rest of the manpage by an empty comment,
like so;

.\" $Id$
.\"

If the immediately preceding comment is a @(#) format ID marker than the
the $Id$ will line up underneath it with no intervening blank lines.
Otherwise, an additional blank line is inserted.

Approved by: bde

Fixed #include(s) in the synopsis to actually declare the function(s) in the
synopsis.

Add boot(9) Obtained from NetBSD w/modifications by me.