Fail. Interrupt loop during install.

[Mark Kahrs <mark.kahrs%gmail.com@localhost>]

after futzing around with netboot installation (and, for the record, the
existing installation documentation is seriously out of date), I
finally got the install
 file to boot, only to eventually encounter an infinite loop of :

stray interrupt: vector 0x18, ipl 31

And, to make matters worse, this was reported *nearly 3 years ago* by
a SIMH user:

http://mailman.trailing-edge.com/pipermail/simh/2013-July/012551.html

This is actual hardware: a 3100 model 38.  If netbsd is not ready for
prime time, perhaps the vax branch should be dropped.  The mop
bootloader has to be obtained from 1.5 and that ain't right.