Thread->getMessages() should not be overwritten by doctrine:generate:entities

I'm working on Symfony 2.1.5-DEV and Doctrine as ORM.
I followed the documentation on `Creating concrete model classes` and then I run `app/console doctrine:generate:entities [...]`.

In my `src/Acme/MessageBundle/Entity/Thread.php` the function `getMessages()` was automatically generated:
```
    /**
     * Get messages
     *
     * @return \Doctrine\Common\Collections\Collection 
     */
    public function getMessages()
    {
        return $this->messages;
    }
```

But in this way it is returning a `Doctrine/Common/Collections/ArrayCollection` instead of an simple array, as set in [Thread.php#L164](https://github.com/FriendsOfSymfony/FOSMessageBundle/blob/master/Model/Thread.php#L164):
```
    /**
     * @see FOS\MessageBundle\Model\ThreadInterface::getMessages()
     */
    public function getMessages()
    {
        return $this->messages->toArray();
    }
```

Doing so, [reset($messages) in Thread.php#L178](https://github.com/FriendsOfSymfony/FOSMessageBundle/blob/master/Model/Thread.php#L178) and [end($messages) Thread.php#L188](https://github.com/FriendsOfSymfony/FOSMessageBundle/blob/master/Model/Thread.php#L188) would return a `Doctrine/Common/Collections/ArrayCollection` object instead of a simple object, and [thread.lastMessage.id in threads_list.html.twig#L39](https://github.com/FriendsOfSymfony/FOSMessageBundle/blob/master/Resources/views/Message/threads_list.html.twig#L39) and [$thread->getFirstMessage() in ThreadManager.php#L346](https://github.com/FriendsOfSymfony/FOSMessageBundle/blob/master/EntityManager/ThreadManager.php#L346) would have problems because expecting an object instead of an ArrayCollection.

My solution is to propose that `getMessages()` in `src/Acme/MessageBundle/Entity/Thread.php` should not be overwritten by automatically generated functions when running `app/console doctrine:generate:entities`; and to achieve this by adding
```
public function getMessages()
{
    return parent::getMessages();
}
```
in the documentation.