Update install.php

fixes "Class Session not found" error while installing

Author: Haikuch

install.php

@@ -41,6 +41,7 @@
 require(PATH_DB . 'nbxml.class.php');
 require(PATH_DB . 'db_posts.class.php');
 require(PATH_KERNEL . 'plugin.class.php');
+require(PATH_HELPERS . 'session.class.php');
 require(PATH_HELPERS . 'crypt.class.php');
 require(PATH_HELPERS . 'date.class.php');
 require(PATH_HELPERS . 'filesystem.class.php');