Improving the management of the collection form type

It just work with country form, it looks like :
![country](https://f.cloud.github.com/assets/3585922/1582019/5d93c786-51e4-11e3-8152-950924c99184.png)

@jjanvier, @pjedrzejewski, @stloyd : Do you like it? Feedback are welcome! Thanks