Fix precompile_smarty3.php

The Smarty class is in the Smarty namespace, and should not be loaded
manually, but through composer. This is taken care of by requiring
`boot.php`. Also make the script slightly more robust as to where it is
invoked from.

util/precompile_smarty3.php

@@ -4,12 +4,11 @@
 * @package util
 */
 
-require_once('boot.php');
-require_once('vendor/smarty/smarty/libs/Smarty.class.php');
+require_once dirname(__DIR__) . '/boot.php';
 
 $folders = array_merge(array('view/tpl/'), glob('view/theme/*/tpl/*', GLOB_ONLYDIR));
 
-$s = new Smarty();
+$s = new \Smarty\Smarty();
 
 $s->setTemplateDir($folders);