title: DataSet.writexml date format issue
body: <p>I am using the <code>dataset.writexml</code> method to generate the XML by executing a query on the MySql database and the query has a date field. When I generate the XML the field value '2012-05-13' is getting converted to as </p>
  
  <pre><code>&lt;orderdate&gt;
    &lt;Year&gt;2013&lt;/Year&gt; 
    &lt;Month&gt;5&lt;/Month&gt; 
    &lt;Day&gt;23&lt;/Day&gt; 
    &lt;Hour&gt;0&lt;/Hour&gt; 
    &lt;Minute&gt;0&lt;/Minute&gt; 
    &lt;Second&gt;0&lt;/Second&gt; 
    &lt;Millisecond&gt;0&lt;/Millisecond&gt; 
  &lt;/orderdate&gt;
  </code></pre>
  
  <p>I want this to be formatted as </p>
  
  <pre><code>&lt;orderdate&gt;2012-05-13&lt;/orderdate&gt; 
  </code></pre>
  
  <p>instead of the above format.</p>