now marked busy as long as it's being in non-reset state, and the
drives are busy as long as at least one instance is open.
Also reformat everything to fit into 80 columns again.
Changed my mind wrt. error reporting for a write-protected drive and
an open() with write intent; ENXIO has been too weird, now return EIO.
Some portions of the code need to be rewritten to use tprintf()
instead of simple printf()'s, so the messages will also appear on the
session terminal, however.
dc16046f96