INT 17 - Alloy NTNX, MW386 - GET USER NUMBER AND CURRENT PRINTER
        AH = 91h
        AL = mode
            00h NTNX compatibility
                Return: CX = user number (00h = host)
                        DX = currently selected printer number (00h-08h)
            01h MW386
                Return: CX = user number
                        DX = physical dev number of currently selected printer
            02h MW386 v2+
                BX = logical device number
                    00h-03h = LPT1-LPT4
                    04h-07h = COM1-COM4
                Return: CX = user number
                        DX = physical device number
Return: AL = status (see AH=81h)