title: Jackson xml serialize map that key contains whitespace
body: <p>i use Jackson 2.5.2 and i have a <code>map&lt;String,String&gt;</code></p>
  
  <p>by default, Jackson serializes it into :</p>
  
  <pre><code>&lt;MyObject&gt;
   &lt;map&gt; 
    &lt;key1&gt;value1&lt;/key1&gt; 
    &lt;key2 containing spaces&gt;value2&lt;/key2 containing spaces&gt;
   &lt;map&gt;
  &lt;/MyObject&gt;
  </code></pre>
  
  <p>but i want a generic xml tag :</p>
  
  <pre><code>&lt;MyObject&gt;
   &lt;map&gt; 
    &lt;entry key="key1"&gt;value1&lt;/entry&gt;
    &lt;entry key="key2 containing spaces"&gt;value2&lt;/entry&gt;
   &lt;map&gt;
  &lt;/MyObject&gt;
  </code></pre>
  
  <p>in this way my xml tags are generic and can be validated with xsd</p>
  
  <p>here is my test</p>
  
  <pre><code>class MyObject {
      Map map = new HashMap();  
      public Map getMap() { return map;}
  }
  // Test
  ObjectMapper xmlMapper = new XmlMapper();
  MyObject myObject = new MyObject();
  myObject.getMap().put("key1","value1");
  myObject.getMap().put("key2 containing spaces","value2");
  System.out.println(xmlMapper.writeValueAsString(myObject));
  </code></pre>
  
  <p>is there any configuration to tell Jackson to serialize generic xml?</p>