Raw tape buffer vs record size

[Steven M. Haflich]

Guy Harris says:
	The most likely reason why the buffer size and address must be
	even when reading from tapes is that "physio" is too dumb to
	realize that tape controllers can be given an odd byte count or
	address.
Long ago, for a very good reason which I can no longer remember, we
hacked a PDP11 V7 tm.c to permit raw device reads and writes with odd
blocksize.  It worked like a charm, and at the time, we were satisfied
that the change would be completely upward compatible.  I don't
remember the exact source changes, but they were indeed simple.