[formrenderers] if a tag object gets there, it blows (closes #2410462)
- cwtags monkeypatches cubicweb's UStringIO's .write and .getvalue methods
- but it cannot monkeypatch list.append ...
<div id="ajaxroot">
<div class="ajaxHtmlHead">
<script src="http://foo.js" type="text/javascript"> </script>
<link rel="stylesheet" type="text/css" media="all" href="qunit.css" />
</div>
<h1>Hello</h1>
</div>