INT 31 P - CauseWay - "LockMem" - LOCK REGION OF MEMORY
	AX = FF1Bh
	BX:CX = starting linear address
	SI:DI = size of region in bytes
Return: CF clear if successful
	CF set on error
Desc:	prevent memory from being 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 locked as well
SeeAlso: AX=FF1Ch,AX=FF1Dh