Thumbnails do not support offset

Created by: graingert

This fails

        <ul class="thumbnails">
            <li class="span4">
             <div class="thumbnail">
                    test
               </div>
           </li>
            <li class="span4 offset4">
             <div class="thumbnail">
                                      test
             </div>
           </li>
        </ul>

However

<div class="row">
    <div class="span4">test</div>
    <div class="span4 offset4">test</div>
</div>

works