Function  10h  Close File                                              (FCB)
     Closes a File After a File Write  
entry   AH      10h 
	DS:DX   pointer to an opened FCB 
return  AL      00h     if the file is found and closed 
		0FFh    if the file is not found in the current directory 
note 1) This function call must be done on open files that are no longer needed, 
	and after file writes to insure all directory information is updated.  
     2) If the file is not found in its correct position in the current  
	directory, it is assumed that the diskette was changed and AL returns  
	0FFh. This error return is reportedly not completely reliable with DOS 
	version 2.x. 
     3) If found, the directory is updated to reflect the status in the FCB, the 
	buffers to that file are flushed, and AL returns 00h.