Update include/serendipity_smarty_class.inc.php

added smarty BC function get_template_vars()

relies on some additional plugins like serendipity_event_autotitle.php, serendipity_event_multilingual, serendipity_event_sidebarhider, serendipity_event_downloadmanager, serendipity_event_microformats and possibly also more plugins by custom developers.