added failing test on form.elements

form.elements[name] property should return array, if the name is provided by more elements (e. g. radio buttons). However, it does not.
Test case that exposes this behaviour has been added.

I used a simple script to test the implementation across browsers, it works the same as far back as IE 5 compatibility mode:
http://jsfiddle.net/nP3SB/1/