[Coco] NitrOS-9 Level 1 for Dragon Tano

[Ken H.]

I have managed to build NitrOS9 Level 1/6809 for the Dragon Tano!
It seems that the Tano Dragon build is broken starting from revision 2620.
After restoring back to the state of version 2619, dated 22 Feb. 2012, I
was able to build working Tano Dragon boot disks!
Ironically, revision 2620 which has the description "Everything WORKS" has
broken the Tano Dragon support.
This seems to be a separate issue from the Coco drive descriptor bug.