Issue #1354726 by develCuy, gnuget, droplet: Add more indexes on {forum_index()}.

core/modules/forum/forum.install

@@ -219,6 +219,8 @@ function forum_schema() {
     ),
     'indexes' => array(
       'forum_topics' => array('nid', 'tid', 'sticky', 'last_comment_timestamp'),
+      'created' => array('created'),
+      'last_comment_timestamp' => array('last_comment_timestamp'),
     ),
     'foreign keys' => array(
       'tracked_node' => array(