The EXB-200 library prints a warning message on its LCD display, when
the tape heads need to be cleaned.  I haven't yet discovered how to detect
dirty tape heads from an application program.  The ioctl/MTIOCGET interface,
which uses the st device driver, doesn't obtain the tape head dirty/clean
status.  The mt command seems to the same info as MTIOCGET.  The LTO-3
SCSI interface manual describes protocols for obtaining cleaning information.
