Function  17h   Rename File Specified by File Control Block              (FCB) 
      Renames file in current directory 
entry   AH      17h 
	DS:DX	pointer to an Struct -FCB (see note 4)
return  AL      00h     successfully renamed 
		0FFh    file not found or filename already exists 
note 1) This service cannot rename read-only files 
     2) The "?" wildcard may be used. 
     3) If the "?" wildcard is used in the second filename, the corresponding  
	letters in the filename of the directory entry are not changed. 
     4) The FCB must have a drive number, filename, and extension in the usual 
	position, and a second filename starting 6 bytes after the first, at  
	offset 11h. 
     5) The two filenames cannot have the same name. 
     6) FCB contains new name starting at byte 17h.