[ticket/11495] Add forum implementation of nestedset

PHPBB3-11495

phpBB/includes/nestedset/exception.php

@@ -0,0 +1,20 @@
+<?php
+/**
+*
+* @package Nested Set
+* @copyright (c) 2013 phpBB Group
+* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
+*
+*/
+
+/**
+* @ignore
+*/
+if (!defined('IN_PHPBB'))
+{
+	exit;
+}
+
+class phpbb_nestedset_exception extends \Exception
+{
+}