title: dynatree selectmode=3 is not honoured when using lazy loading
body: <p>I was trying to use dynatree with lazy loading on in my project.
  When I tried to combine the select functionality with the checkboxes and select mode 3 I was disappointed to see that the select rule for mode 3 which is select everything including children children .... children when the parent is selected.
  This is because the children havent yet been loaded.</p>
  
  <p>Does anyone have a workaround to get this working ? I would very much appreciate any suggestions.
  Zank ya!!</p>