add missing file header

lib/private/db/connectionwrapper.php

 <?php
+/**
+ * Copyright (c) 2013 Thomas Müller <deepdiver@owncloud.com>
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
 
 namespace OC\DB;