Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Move most of the remaining USD/PSD/SMM papers into share/doc

For variables that are only checked with defined(), don't provide
any fake value.

bsd.doc.mk changes:

Don't gratuitously pipe thru a cat(1) if NODOCCOMPRESS.

Only create _stamp.extra when necessary.

Get rid of SOELIMPP and OBJS.

Use Groff version of soelim(1); we need its -I option
for the following to work.

Don't needlessly chdir to SRCDIR. Only a few documents
need CD_HACK, and those that need it either use refer(1)
or .PSPIC macro which internally uses the .psbb call.

$Id$ -> $FreeBSD$

Revert $FreeBSD$ back to $Id$

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.

Make these documents build if possible.