INT 10 - VIDEO - READ LIGHT PEN POSITION (except VGA)

	AH = 04h
Return: AH = light pen trigger flag
	    00h not down/triggered
	    01h down/triggered
		DH,DL = row,column of character light pen is on
		CH = pixel row (graphics modes 04h-06h)
		CX = pixel row (graphics modes with >200 rows)
		BX = pixel column
Desc:	determine the current position and status of the light pen (if
	  present)
Notes:	on a CGA, returned column numbers are always multiples of 2 (320-
	  column modes) or 4 (640-column modes)
	returned row numbers are only accurate to two lines