INT 21 U - OS/2 v1.x FAPI - OS/2 FILE SYSTEM JOIN/SUBST                         
	AH = 61h
	BP = 6467h ("dg")
	AL = function
	    00h list (i.e. get)
	    01h add
	    02h delete
	BX = drive number
	CX = size of buffer
	SI = type (0002h JOIN, 0003h SUBST)
	ES:DI -> buffer
Return: CF clear if successful
	    AX = 0000h
	    ES:DI buffer filled, if appropriate
	CF set on error
	    AX = error code
Notes:	used by JOIN and SUBST to communicate with the OS/2 file system
	for function 00h (list), the ES:DI buffer is filled with the ASCIZA NUL-terminated ASCII string.	The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h.  Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL.
	  JOIN/SUBST path or an empty string if the drive is not JOINed/SUBSTed
	also supported by OS/2 v2.0+ Virtual DOS Machines