I've added tape device compression enable/disable (a command part of the
MTIOCTOP ioctl only).

I've also added SCSI logical block locate and SCSI hardware block locate.

I've modified the SCSI tape driver and the mt(1) command to exercise these
features, as well as updated some man pages.

I've done some testing, but the sooner folks look at this and tell me where
I putzed, the quicker I can fix it.

-matt