INT 31 - CauseWay - "UnLockMem" - UNLOCK REGION OF MEMORY

	AX = FF1Dh
	BX:CX = starting linear address
	SI:DI = size of region in bytes
Return: CF clear if successful
	CF set on error
Desc:	allow memory to be swapped out by the virtual memory manager
Note:	locks are applied on 4K page boundaries, so memory above and below
	  the specified region may be unlocked as well
SeeAlso: AX=FF1Bh,AX=FF1Eh