INT F1 - Common ISDN API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes. (CAPI) v2.0 - "CAPI_SET_SIGNAL" - SIGNAL HANDLING
	AL = 05h
	AH = CAPI version number * 10 (14h for v2.0)
	DX = application ID (see AH=01h)
	ES:BX -> signal handler or 0000h:0000h to disable
	SI:DI = parameter to pass to signal handler
Return: AX = status (0000h,11xxh) (see #04070)
Notes:	the caller is required to provide at least 512 bytes of stack space
	the signal handler is called as though it were an interrupt, with
	  interrupts disabled and DX,SI,DI set as they were when this function
	  was called; the handler must preserve all registers and return with
	  an IRET
	the signal handler may call CAPI_PUT_MESSAGE, CAPI_GET_MESSAGE, and
	  CAPI_SET_SIGNAL
SeeAlso: INT F1/AL=01h