INT 15 - HUNTER 16 - SET INT 72h VECTOR                                         
	AH = 87h
	DS:DX = new service routine
Desc:	set the INT 72h vector which is called in 2 cases:
	  - when the machine is about to turn off or reboot, INT 72h is called
	    with AH=0
	  - when the machine is powering up INT 72h is called with AH=01h
Note:	the actual INT 72h vector must also be changed with INT 21/AH=25h