title: xml error: Non white space characters cannot be added to content
body: <p>I am trying to open an xmldocument like this:</p>
  
  <pre><code>var doc = new XDocument("c:\\temp\\contacts.xml");
  var reader = doc.CreateReader();
  var namespaceManager = new XmlNamespaceManager(reader.NameTable);
  namespaceManager.AddNamespace("g", g.NamespaceName);
  var node = doc.XPathSelectElement("/Contacts/Contact/g:Name[text()='Patrick Hines']", namespaceManager);
  node.Value = "new name Richard";
  doc.Save("c:\\temp\\newcontacts.xml");
  </code></pre>
  
  <p>I returns an error in the first line:</p>
  
  <pre><code>Non whitespace characters cannot be added to content.
  </code></pre>
  
  <p>The xmlfile looks like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;Contacts xmlns:g="http://something.com"&gt;
    &lt;Contact&gt;
      &lt;g:Name&gt;Patrick Hines&lt;/g:Name&gt;
      &lt;Phone&gt;206-555-0144&lt;/Phone&gt;
      &lt;Address&gt;
        &lt;street&gt;this street&lt;/street&gt;
      &lt;/Address&gt;
    &lt;/Contact&gt;
  &lt;/Contacts&gt;
  </code></pre>