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

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

Per email to arch@ a little while ago (that was greeted with silence),
prefer the more common > ${.TARGET} over > opt_foo.h in modules
makefiles.

Let modules use the kernel's opt_*.h files if built along with
the kernel by wrapping all targets for fake opt_*.h files in
.if defined(KERNBUILDDIR). Thus, such fake files won't be
created at all if modules are built with the kernel.

Some modules undergo cleanup like removing unused or unneeded
options or .h files, without which they wouldn't build this way
or the other.

Reviewed by: ru
Tested by: no binary changes in modules built alone
Tested on: i386 sparc64 amd64

Mechanically tidy up the contents of CLEANFILES:M*.h: kmod.mk
automatically removes opt_*.h and if_*.h found in SRCS.

Clean CLEANFILES.

bsd.kmod.mk does not deal with manpages anymore.

Updated cx driver commit part 1: bring in the new kernel driver.

This is the vastly updated cx drvier from Roman Kurakin <rik@cronyx.ru>
who has been patiently waiting for this update for sometime.

The driver is mostly a rewrite from the version we have in the tree.
While some similarities remain, losing the little history that the old
driver has is not a big loss, and the re@ felt it was easier this way (less
error prone).

The userland parts of this update will be committed shortly.

The driver is not connected to the build yet. I want to make sure I
don't break any platform at any time, so I want to test that with
these files in the tree before I continue (on the off chance I'm
forgetting a file).

I changed the DEBUG macro to CX_DEBUG from the code that was submitted
(to not break when we go to building with opt_global.h after the
release), as well adding $FreeBSD$.

Submitted by: Roman Kurakin
Approved by: re@ <scottl>