Declaring namespaces in the Symfony >=2.1 way

I think the installation documentation should be updated.

```php
<?php
// app/autoload.php
$loader->registerNamespaces(array(
    // ...
    'Knp\Bundle' => __DIR__.'/../vendor/bundles',
    'Knp\Menu'   => __DIR__.'/../vendor/KnpMenu/src',
    // ...
));
```

This seems to be the Symfony 2.0 way of declaring namespaces. Now we should have
```php
<?php
// intl
if (!function_exists('intl_get_error_code')) {
	$loader->add('Knp\Bundle', __DIR__.'/../vendor/bundles');
	$loader->add('Knp\Menu', __DIR__.'/../vendor/KnpMenu/src');
	// … other declarations
}
```

My 2 cents

Guillaume