INT 31 - CauseWay v1.3 - "GetMCBSize" - GET CURRENT MCB ALLOCATION BLOCK SIZE

	AX = FF27h
Return: ECX = current threshold
Desc:	determine the memory allocation size below which CauseWay will use
	  internal MCB chains rather than allocating full 4K pages via DPMI
SeeAlso: AX=FF00h,AX=FF28h