Use "RCS tag" instead of "$FreeBSD$ tag", since svn will obediently
expand the latter.

MFC after:	3 days
Remove the old NFS client and server from head,
which means that the NFSCLIENT and NFSSERVER
kernel options will no longer work. This commit
only removes the kernel components. Removal of
unused code in the user utilities will be done
later. This commit does not include an addition
to UPDATING, but that will be committed in a
few minutes.

Discussed on: freebsd-fs
Add an UPDATING entry for r276096, which removed the kernel
sources for the old NFS client and server.
Allow ktr(4) tracing of all guest exceptions via the tunable
"hw.vmm.trace_guest_exceptions".  To enable this feature set the tunable
to "1" before loading vmm.ko.

Tracing the guest exceptions can be useful when debugging guest triple faults.

Note that there is a performance impact when exception tracing is enabled
since every exception will now trigger a VM-exit.

Also, handle machine check exceptions that happen during guest execution
by vectoring to the host's machine check handler via "int $18".

Discussed with:	grehan
MFC after:	2 weeks
Temporarily disable the cpus directive until I figure out what's wrong.