title: jsTree: with lazy loading the plugin "dnd" is not working
body: <p>I'm using jsTree (latest version) in my web app. I have a lot of nodes to display in the tree, so I am using lazy loading otherwise I would run into a time out.
  When the tree is loaded, the user can pick values from a second tree and move them into the lazy loaded tree (jsTree plugin "dnd"). Both tree have the jsTree plugin "dnd" installed. But I can not drop a element into the lazy loaded tree, when I try to do so the node to be dropped is having an icon with a red cross (indication: not allowed here).</p>
  
  <p>This is the code for the lazy loaded tree:</p>
  
  <pre><code>$('#target_tree').jstree({
    'core' : {
      'data' : {
        "url" : "get_current_hierachy",
        "data" : function (node) {
          return {'p_parent_id': node.id};
        },
        "dataType": "json",
        "check_callback": true
      }
    },
    "plugins" : ["dnd"]
  });
  </code></pre>
  
  <p>When I load some data in the first tree without the lazy loading, the drag'n'drop is working as expected.
  When I load data in the first tree with lazy loading, the drag'n'drop is not working any more.</p>
  
  <p>Any help would be greatly appreciated.</p>