title: Add a date picker to system.xml on custom module
body: <p>As stated in the subject, I am trying to add a date field with its date picker in the System > Configuration area for a custom module (thus using etc/system.xml).</p>
  
  <p>I tried to get inspiration from the thread below : 
  <a href="https://stackoverflow.com/questions/3054429/magento-add-a-button-to-system-xml-with-method-attached-to-it">Magento - Add a button to system.xml with method attached to it</a></p>
  
  <p>but no success.</p>
  
  <p>I'm sure this is a question of creating the right block or method to create a custom html field but I cannot read thru the Magento Matrix :)</p>
  
  <p>I am stuck at the step where I need to code the  class (Datefield.php): </p>
  
  <pre><code>    &lt;?php
              class Namespace_Module_Block_Datefield extends Mage_Adminhtml_Block_System_Config_Form_Field {
  
               protected function _getElementHtml(Varien_Data_Form_Element_Abstract $element) {
      // ----&gt; Am I wrong in calling ..._Abstract?  Should I call Varien_Data_Form_Element_Date? I've tried but no success either...
  
  $this-&gt;setElement($element);
  
                $html = // ------------------&gt; what to put here? Call a block or some other method?
                        -&gt;setFormat('d-m-Y')
                        -&gt;setLabel($this-&gt;__('Choose date'))
                        -&gt;toHtml();
  
                return $html;
               }
              }    
              ?&gt;
  </code></pre>
  
  <p>Do you have a trick on how to do that ?</p>
  
  <p>Thanks a lot.
  Hervé</p>