INT 67 - LIM EMSsee Expanded Memory Specification 4.0 - ENABLE/DISABLE OS FUNCTION SET FUNCTIONS
	AH = 5Dh
	AL = subfunction
	    00h enable OS Function Set
	    01h disable OS Function Set
	    02h return access key (resets memory manager, returns access key at
		next invocation)
	BX,CX = access key returned by first invocation
Return: BX,CX = access key, returned only on first invocation of function
	AH = status (see also AH=5Ch)
	    8Fh undefined subfunction
	    A4h operating system denied access