tu80 problem

[obrien at Rand-Unix.ARPA]

	TU80's are not the only drives with this problem.  Our "dump"
program (4.1) also overshot some of our tapes.  I checked the code, and
after some arithmetic and checking of specifications I decided that it was
correct.  So either the specs are wrong (cumulative error over 2400'), or
some tapes just come short from the manufacturer.

	We use shell scripts to do dumps and I just added a flag to tell
"dump" that the tape was about 2300' long, and everything works fine now.
Our drive is a TU45.  I think we just went ahead and did the same thing
with our TU78 when we installed scripts for that system, so I don't know
if things come up short over there or not.  Anyway, it's a problem.