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)

update smp related documentation after recent changes

Remove references to machdep.hlt_logical_cpus and
machdep.hlt_cpus sysctls and tunables.
Document machdep.hyperthreading_allowed and
hint.lapic.X.disabled tunables.

Prompted by: ru
Proofreading: bf
Reviewed by: jhb
Approved by: re (kib)

Add sysdoc, a small set of scripts which will parse a kernel binary and
modules to rip out the available sysctls. It will then produce a manual
page which may be installed with 'make install'. Currently typing 'make'
in the directory uses the default /boot/kernel files. To use a specific
directory, run sysdoc -k [location].