INT 31 P - CauseWay v1.3 - "GetMemSO" - ALLOCATE MEMORY AND RETURN SEL:OFFSET
	AX = FF2Ch
	CX:DX = block size in bytes
Return: CF clear if successful
	   SI:DI = selector:offset of allocated memory
	CF set on error
Note:	unlike "GetMem" (AX=FF0Bh), this function will reuse selectors until a
	  segment is full, rather than allocating a new selector for each
	  memory block
SeeAlso: AX=FF00h,AX=FF2Dh,AX=FF2Eh