INT 21,49 - Free Allocated Memory

	AH = 49h
	ES = segment of the block to be returned (MCB + 1para)

	on return:
	AX = error code if CF set  (see DOS ERROR CODES)

	- releases memory and MCB allocated by INT 21,48
	- may cause unpredictable results is memory wasn't allocated using
	  INT 21,48 or if memory wasn't allocated by the current process
	- checks for valid MCB id, but does NOT check for process ownership
	- care must be taken when freeing the memory of another process, to
	  assure the segment isn't in use by a TSR or ISR
	- this function is unreliable in a TSR once resident, since
	  COMMAND.COM and many other .COM files take all available memory
	  when they load
	- see  INT 21,4A