normalize value on newElement

normalize value on newElement for radio and checkbox type, to fix
default value when not defined.
http://www.w3.org/TR/html5/forms.html#dom-input-value-default-on
Added specs to double check the values
Improvements after review sugestions
Merge pull request #2584 from SergioCrisostomo/checkbox-newElement-value-fix

normalize values on newElement for radio and checkbox types - Fix #2538