我正在尝试在没有供应商的情况下安装 symfony2，并且在运行 app_dev.php 时不断收到以下错误：
RuntimeException: The autoloader expected class "Symfony\Component\EventDispatcher\Event" to be defined in file "/var/www/caremonk/vendor/symfony/symfony/src/Symfony/Component/EventDispatcher/Event.php". The file was found but the class was not in it, the class name or namespace probably has a typo.
我已经通过以下方式安装了正确的文件和供应商： php composer.phar update php composer.phar install
我还检查了 Symfony2 抱怨的文件，文件的内容是：
<?php
/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace Symfony\Component\EventDispatcher;
/**
* Event is the base class for classes containing event data.
*
* This class contains no event data. It is used by events that do not pass
* state information to an event handler when an event is raised.
*
* You can call the method stopPropagation() to abort the execution of
* further listeners in your event listener.
*
* @author Guilherme Blanco <guilhermeblanco@hotmail.com>
* @author Jonathan Wage <jonwage@gmail.com>
* @author Roman Borschel <roman@code-factory.org>
* @author Bernhard Schussek <bschussek@gmail.com>
*
* @api
*/
class Event
{
// Some more code
}
这是我没有接触过的标准 symfony2 类，所以我对我需要做的事情有点迷茫。我怎样才能摆脱这个错误？