Change button checkbox/radios to ignore hidden input fields

Created by: mvastola

Allows for HTML like:

<div class="btn-group-toggle" data-toggle="buttons">
  <label class="btn btn-info">
    <input name="checkbox" type="hidden" value="0">
    <input id="cb" name="checkbox" type="checkbox" value="1" autocomplete="off"> Click Me
  </label>
</div>

Fixes #27795 (closed)