title: update an attribute value using wildcards
body: <p>I would have thought that if you didn't provide a destination, xmltask would modify the source file and replace it, but apparently that's not the case since the below code does not work:</p>
  
  <pre><code>&lt;xmltask source="**\plugin.xml"&gt; 
      &lt;attr path="plugin" attr="version" value="12345" /&gt; 
  &lt;/xmltask&gt;
  </code></pre>
  
  <p>If I specify a destination, I get an error saying "Multiple inputs, but only one destination":</p>
  
  <pre><code>&lt;xmltask source="**\plugin.xml" dest="**\plugin.xml"&gt; 
      &lt;attr path="plugin" attr="version" value="12345" /&gt; 
  &lt;/xmltask&gt;
  </code></pre>
  
  <p>How can I get this to work with wildcards? Is it possible?</p>