truncate sys_session during update

install/lib/update.lib.php

@@ -394,6 +394,9 @@ function updateDbAndIni() {
 	unset($old_ini_array);
 	unset($tpl_ini_array);
 	unset($new_ini);
+
+	// Truncate sys_session
+	$inst->db->query("TRUNCATE sys_session");
 }