PHP 5 Autoloader with Namespace support

Autoloader.php

<?php
class Autoloader
{
    protected $directory;

    protected $methodQueue;

    /**
     * @param string $dir the directory to look from
     */
    public function __construct($dir) {
        if(is_dir($dir)) {
          $this->directory = $dir;
        } else {
            require_once 'Exception.php';
            throw new AutoloadException("Autoloader directory does not exist");
        }
        $this->methodQueue = new \SplQueue();
    }

    /**
     * @param string $cls the class that could not be found
     */
    public function includeClass($cls) {
        $file = str_replace("\\",DIRECTORY_SEPARATOR,$cls);
        $path = $this->directory . DIRECTORY_SEPARATOR . $file . '.php';
        if (file_exists($path)) {
            require_once $path;
        }
    }

    /**
     * Add a method to the queue. All methods in the queue will
     * be executed before the default includeClass method is registered
     * @param $cb a callback to be executed
     */
    public function addMethod($cb) {
        $this->methodQueue->enqueue($cb);
    }

    public function register() {
        $this->methodQueue->rewind();
        while($this->methodQueue->current()) {
            call_user_func($this->methodQueue->dequeue());
        }
        spl_autoload_register(array($this,'includeClass'));
    }
}