fix bug 169 when removing a node, be sure to also remove the drag and drop reference

src/DragAndDrop.js

@@ -145,6 +145,7 @@
         this.off('mousedown.kinetic');
         this.off('touchstart.kinetic');
     };
+
     /**
      * get draggable.  Alias of getDraggable()
      * @name isDraggable

src/Node.js

@@ -167,6 +167,12 @@
                 parent.children.splice(this.index, 1);
                 parent._setChildrenIndices();
 
+                // remove from DD
+                var dd = Kinetic.DD;
+                if(dd && dd.node && dd.node._id === this._id) {
+                    delete Kinetic.DD.node;
+                }
+
                 // remove children
                 while(this.children && this.children.length > 0) {
                     this.children[0].remove();