INT 21 - European MS-DOS 4.0 - SET SIGNAL HANDLER                               
	AH = 8Ch
	AL = signal number (see #01793)
	BL = action (see #01794)
	DS:DX -> signal handler (see #01795)
Return: CF clear if successful
	    AL = previous action
	    ES:BX -> previous signal handler
	CF set on error
	    AX = error code (01h,invalid SigNumber or Action)
		  (see #01680 at AH=59h/BX=0000h)
Desc:	set the routine which will be invoked on a number of exceptional
	  conditions
Note:	all signals will be sent to the most recently installed handler
SeeAlso: AH=8Dh


(Table 01793)
Values for European MS-DOS 4.0 signal number:
 01h	SIGINTR		Control-C or user defined interrupt key
 08h	SIGTERM		program termination
 09h	SIGPIPE		broken pipe
 0Dh	SIGUSER1	reserved for user definition
 0Eh	SIGUSER2	reserved for user definition


(Table 01794)
Values for signal action:
 00h	SIG_DFL		terminate process on receipt
 01h	SIG_IGN		ignore signal
 02h	SIG_GET		signal is accepted
 03h	SIG_ERR		sender gets error
 04h	SIG_ACK		acknowledge received signal and clear it, but don't
			  change current setting


(Table 01795)
Values signal handler is called with:
	AL = signal number (see #01793)
	AH = signal argument
Return: RETF, CF set: terminate process
	RETF, CF clear, ZF set: abort any interrupted system call with an error
	RETF, CF clear, ZF clear: restart any interrupted system call
	IRET: restart any interrupted system call
Note:	the signal handler may also perform a nonlocal GOTO by resetting the
	  stack pointer and jumping; before doing so, it should dismiss the
	  signal by calling this function with BL=04h