THIS ROUTINE, USED IN VIRTUAL DISKS, DEASSIGNS A VIRTUAL DISK.

A GOOD METHOD OF DOING THIS, PLUS DELETING THE VIRTUAL DISK, IS GIVEN IN
THE BELOW @ COMMAND FILE, ASSUMING YOUR VIRTUAL DISKS ARE IN [0,0].

.ENABLE SUBSTITUTION
.ASKN [0:17:2] VD VD
DVD VD'VD':
.ASKN [0:2:0] DR DR
.ASKS NAME NAME
PIP DR'DR':[0,0]'NAME'.DSK;1/PR/SY:REWD
PIP DR'DR':[0,0]'NAME'.DSK;1/DE
PIP DR'DR':/FR