目錄檔案瀏覧

1. moodle 2.3 版中的目錄檔案瀏覧，使用者無法更動其排序方式，預設順序為 sortorder, itemid, filepath, filename，增加以修改時間遞減 timemodified DESC 優先排列。

   [root@dywang moodle23]# diff -uN ../moodle23.bak/lib/filestorage/file_storage.php lib/filestorage/file_storage.php 
   --- ../moodle23.bak/lib/filestorage/file_storage.php	2012-07-06 08:44:15.000000000 +0800
   +++ lib/filestorage/file_storage.php	2017-08-04 09:15:06.024609587 +0800
   @@ -443,7 +443,7 @@
         */
        public function get_area_tree($contextid, $component, $filearea, $itemid) {
            $result = array('dirname'=>”, 'dirfile'=>null, 'subdirs'=>array(), 'files'=>array());
   -        $files = $this->get_area_files($contextid, $component, $filearea, $itemid, "sortorder, itemid, filepath, filename", true);
   +        $files = $this->get_area_files($contextid, $component, $filearea, $itemid, "timemodified DESC, sortorder, itemid, filepath, filename", true);
            // first create directory structure
            foreach ($files as $hash=>$dir) {
                if (!$dir->is_directory()) {