title: WPF toolkit DatePicker change default value 'show calendar'
body: <p>I'm using the latest <strong>WPF toolkit</strong>, specifically the <code>DatePicker</code>. Everything works fine, but when no value is provided, the default 'SHOW CALENDAR' text appears in the DatePickerTextBox.
  I want to be able to change this value in WPF. </p>
  
  <p>One told me to download the source, add a new Dependency property and recompile to dll. That's cool but what if new version is released? </p>
  
  <p>That's why I'd like to template this control in that way, that I'll be able to override this default string. Any idea how to do that?</p>
  
  <p>Thanks!</p>