Updating Request::execute

Does not make much sense to throw an exception BEFORE the beginning of the project code. So just create artificial Response with the appropriate headers, etc.

In general, works the same as before, but this adds ability for creating some error catchers. For example:

```php
<?php
/**
 * HTTP_Exception_401 Class
 *
 * @package    Gleez\HTTP
 * @author     Gleez Team
 * @version    1.0.0
 * @copyright  (c) 2011-2013 Gleez Technologies
 * @license    http://gleezcms.org/license  Gleez CMS License
 */
class HTTP_Exception_401 extends HTTP_Exception {

	/**
	 * HTTP 401 Unauthorized
	 * @var integer
	 */
	protected $_code = 401;

    /**
     * Generate a Response for the 401 Exception.
     * 
     * The user should be redirect to a login page.
     * 
     * @return Response
     */
    public function get_response()
    {
        $response = Response::factory()
            ->status(401)
            ->headers('Location', URL::site(Route::get('user')->uri(array('action' => 'login'))));
 
        return $response;
    }
}
```