added failing test on form.elements

Zombie.js does not support returning radio inputs in form.elements properly. If there are more radio inputs found, form.elements[name] should return array with all of them, however now it does not.

Test case that exposes this behavious has been added.

Screenshot below shows how Chrome (v31) returns array of all radio inputs.

![screen shot 2013-11-19 at 11 34 59](https://f.cloud.github.com/assets/1100170/1571510/d34003d4-5106-11e3-8154-dde7bf924459.png)