We would previously not return a RadioNodeList in the curious case where
a named item resolves to two different elements within the form.
This was not a problem when calling namedItem directly in the IDL as
named_item_or_radio_node_list shadows named_item but is exposed when
calling the property through array bracket notation (as an example).
Fix this, and add a bunch more tests to cover
HTMLFormControlsCollection.
ec2b4c271f