INT E0 - DR Multiuser DOS - "A_SET" - SET DEFAULT AUX DEVICE NUMBER
	CL = A8h
	DL = auxiliary device number
Return: AX = status
	    0000h successful
	    FFFFh failed
	CX = error code
Desc:	specify which physical device will become AUX
SeeAlso: INT E0/CL=A5h,INT E0/CL=A9h