C: made it so column DIR* are not kept open to handle very large DMS

src/obidmscolumndir.h

@@ -40,12 +40,6 @@ typedef struct OBIDMS_column_directory {
 	char		directory_name[OBIDMS_COLUMN_MAX_NAME+1];	     /**< The name of the directory
 	                                     	 	 	 	 	 	  *    containing the column.
 	                                     	 	 	 	 	 	  */
-	DIR*		directory;										 /**< A directory entry usable to
-										 	 	 	 	 	 	  *    refer and scan the column directory.
-										 	 	 	 	 	 	  */
-	int			dir_fd;											 /**< The file descriptor of the directory entry
-																  *   usable to refer and scan the column directory.
-																  */
 } OBIDMS_column_directory_t, *OBIDMS_column_directory_p;