Log Message:
Update to 1.3.8.  Changes:

* New geometry type added: "extsurface", for discs where the sector
 numbers increase across both sides (eg: 1-9 on side 0, 10-18 on
 side 1).

* New backend: IMD (for files created by ImageDisk). Read/write
 support. Also has a built-in extra geometry probe, which may be worth
 pushing to other drivers (eg: DSK, TD0) that carry a similar amount
 of detail.