Switch to XHTML parser for forms to handle self-closing tags.

AIB introduced some new content:

```<select name="selectProduct">
  <option value="0">Select a product:</option>
  <optgroup label="Loans ">
    <option value="onlineloan.htm">Personal / Car Loans</option>
  </optgroup>
  <optgroup label="Savings &amp; Investments-R32">
    <option value="onlinesaver.htm">Online Saver</option>
  </optgroup>
  <optgroup label="Insurance">
    <option value="http://www.aib.ie/personal/insurance/sl-aib-car-insurance ">Car Insurance</option>
    <option value="http://www.aib.ie/personal/insurance/sl-aib-health-insurance">Health Insurance</option>
    <option value="http://www.aib.ie/personal/insurance/sl-aib-home-insurance">Home Insurance</option>
  </optgroup>
  <optgroup label="Credit Cards"/>
  <optgroup label="Mortgages ">
    <option value="mortgages.htm">Mortgage 'Call Back'</option>
  </optgroup>
</select>```

The SGML parser chokes on the self closing "Credit Cards" element.  (actually the form parser dies, because only a closing tag is "seen" by the SGML parser)

The attached change switches to an XHTML parser which handles the self-closing tag correctly.  (I assume it emits an opening and closing tag event for a self-closing element)