[PHP_yaf]Yaf_Application

Yaf_Application::app返回当前的Yaf_Application实例，它实质上是一个单例模式：

<?php
$config = array(
        "ap" => array(
                "directory" => "/usr/local/www/ap",
        ),
);
$app = new Yaf_Application($config);
assert($app === Yaf_Application::app());//返回true
?>