title: (a)Smack's IQ.toXml() returns XML without custom child elements
body: <p>I'm using asmack the latest version (asmack-android-8-source-0.8.3) in a android project and
  I have the following code:</p>
  
  <pre><code>connection.addPacketListener(new PacketListener()
  {
      @Override
      public void processPacket(Packet p)
      {
          if(p.getPacketID().equals("v3"))
          {
              Log.e("TAG", p.toXML());
          }
      }
  }, new IQTypeFilter(IQ.Type.RESULT));
  
  
  Packet iq = new Packet() 
  {
      @Override
      public String toXML() 
      {
          String str = "&lt;iq type='get' id='v3'&gt;&lt;getservertime xmlns='urn:xmpp:mrpresence'/&gt;&lt;/iq&gt;";
          Log.e("TAG", str);
          return str;
      }
  };
  
  //sends &lt;iq type='get' id='v3'&gt;&lt;getservertime xmlns='urn:xmpp:mrpresence'/&gt;&lt;/iq&gt;
  connection.sendPacket(iq);
  </code></pre>
  
  <p>in the debugger the response it's ok and this is expected:</p>
  
  <pre><code>&lt;iq type="result" id="v3" to="minimaal@mrserver/Smack"&gt;
      &lt;servertime xmlns="urn:xmpp:mrpresence" utc="2013-06-28T11:45:32.380Z" local="2013-06-28T07:45:32.380Z"/&gt;
  &lt;/iq&gt;
  </code></pre>
  
  <p>but p.toXML() in the package listner, the tag "servertime" it's missing:</p>
  
  <pre><code>&lt;iq id="v3" to="minimaal@mrserver/Smack" type="result"&gt;&lt;/iq&gt;
  </code></pre>
  
  <p>Any suggestions on what I'm doing wrong?</p>