INT 2F - PC-DOS Econet v1.05 - ADD EVENT HANDLER                                
	AX = C503h
	DS:DX -> event handler (see #03046)
Return: AX = return code (see #03037)
Note:	the interrupt-enable state will be preserved, but interrupts may be
	  enabled during processing of this function
SeeAlso: AX=C500h,AX=C504h,AX=C505h,AX=C508h


Format of Econet event handler:
Offset	Size	Description	(Table 03046)
 00h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	-> next handler's code (at offset 8, filled in by Econet)
 04h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	-> previous event handler (filled in by Econet)
 08h	var	entry point (executable code called on event) (see #03047)


(Table 03047)
Values Econet event handler is called with:
	AL = event number
	AH = timeout flag (01h if timeout, else 00h)
Return:	all registers preserved
	if event trapped by this handler, issue RETF
	if event not trapped, jump to address stored at offset 0
SeeAlso: #03046