(e.g. powerpc64), this looks in a slightly different default path than now,
specifying both $MACHINE and $MACHINE_ARCH:
MIRROR/pub/FreeBSD/releases/`uname -p`/`uname -m`/`uname -r`
How to handle TBEMD properly probably merits some more discussion, but,
since no such 9.0-CURRENT distfiles exist at the moment, all existing
mirrors presently fail anyway.
