freeze after root disk found

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

2 rather different -current/amd64 computers happily run with Friday's code,
but freeze with an hour ago's Jan 20 09:17 GMT code, e.g.:

[     5.390862] boot device: wd0
[     5.390862] root on wd0a dumps on wd0b
[   154.958077] fatal breakpoint trap in supervisor mode

The fatal breakpoint happened when I hit esc-ctrl-alt on the USB keyboard
to try to find out where it had got stuck. Can't savecore the corefile...

Cheers,

Patrick