preserve filename and metadata fields on backup/restore

Most obvious for instances of the module where the icon used in Moodle
on the course page is derived from the filename rather than the mimetype
field, e.g. MP3. The generic icon gets used instead on the restored
resources.

backup/moodle2/backup_equella_stepslib.php

@@ -18,7 +18,7 @@ class backup_equella_activity_structure_step extends backup_activity_structure_s
     protected function define_structure() {
         $equella = new backup_nested_element('equella',
                 array('id'),
-                array('course','name','intro','introformat','timecreated','timemodified','url','mimetype','popup','activation','uuid','version','path','attachmentuuid','ltisalt')
+                array('course','name','intro','introformat','timecreated','timemodified','url','mimetype','popup','activation','uuid','version','path','attachmentuuid','ltisalt','filename','metadata')
         );
         $equella->set_source_table('equella', array('id' => backup::VAR_ACTIVITYID));
         $equella->annotate_files('mod_equella', 'intro', null);