merge r12451 from trunk to branch 2.3

feature:2473
Apply trigger render_element_description for thumbnail title

git-svn-id: http://piwigo.org/svn/branches/2.3@12452 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions.inc.php

@@ -880,7 +880,7 @@ function get_picture_title($info)
 {
   if (isset($info['name']) and !empty($info['name']))
   {
-    return $info['name'];
+    return trigger_event('render_element_description', $info['name']);
   }
 
   return  get_name_from_file($info['file']);