Stacked dump tapes

[Alex White]

Yes, it is about time that the stupid method of dealing with end of tape
on unix disappears.
I have changed the drivers locally as follows
	On the write which passes the EOT mark, normal status is returned.
	i.e. the block was written out correctly.
	On any future write, EEOT is returned, and the block isn't written.
	Thus, ordinary processes which know nothing about tapes run
	correctly, and there is no problem; however since they call perror
	you get a reasonable error message when they die.
	However, for smart processes, you can do a MTIOCEOT which say's
	that you know you've hit the end of tape, but you'd like
	to write out trailer records.  It then lets you do whatever you
	like; even go off the end of the tape.
	On reads, you always get the block, it ignores the end of tape;
	its up to you to verify that correct tape marks were written.
Anyhow, with this actually fairly trivial change, you can now very
easily change dump to correctly handle end of tape.
I have fixes for mt.c and ut.c if anybody wants them; you can of course
also have the fix to dump.