code: function() {
      var oColumn, elTh;
      for(var i=0, len=this._oColumnSet.tree[0].length; i<len; i++) {
          oColumn = this._oColumnSet.tree[0][i];
          if(oColumn._dd) {
              oColumn._dd = oColumn._dd.unreg();
              Dom.removeClass(oColumn.getThEl(), DT.CLASS_DRAGGABLE);       
          }
      }
  }
docs: Disables DD from top-level Column TH elements.
  
  @method _destroyDraggableColumns
  @private