INT 6F - 10NET v3.3+ - UNMOUNT                                                  
	AH = 18h
	AL = local drive number (0=A:)
	BL = type
	    00h	    disk
	    01h-03h LPTn
	    04h,05h COMx
Return: CF clear if successful
	CF set on error
	    AX = error code (see #03740)
SeeAlso: AH=17h