code: function (o,evt,fn) {
          var sub = function () {
              // Unsubscribe myself
              o.unsubscribe(evt, sub);
              // Pass the event handler arguments to the one time callback
              fn.apply({},arguments);
          };
          o.subscribe(evt,sub);
      }
docs: Schedule an event callback that will execute once, then unsubscribe
  itself.
  @method _oneTimeCallback
  @param o {EventProvider} Object to attach the event to
  @param evt {string} Name of the event
  @param fn {Function} function to execute once
  @private