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

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

MF tbemd: Minor tweaks, prefer MACHINE_CPUARCH generally to MACHINE_ARCH

MFp4: add FireWire/dcons support in loader for i386/amd64.

It is disabled by default. You need to put
LOADER_FIREWIRE_SUPPORT=yes in /etc/make.conf
and rebuild loader to enable it.
(cd /sys/boot/i386 && make clean && make && make install)

You can find a short introduction of dcons at
http://wiki.freebsd.org/DebugWithDcons