old_contents: import datetime
  import tornado.gen
  import tornado.ioloop
  
  
  def delay(dur, callback=None):
      """Delay N seconds. This must be invoked as
      yield tornado.gen.Task(app.delay, dur)
      """
      delta = datetime.timedelta(seconds=dur)
      return tornado.ioloop.IOLoop.current().add_timeout(delta, callback)
  
new_contents: import datetime
  import tornado.gen
  import tornado.ioloop
  
  
  def delay(dur, callback=None):
      """Delay N seconds. This must be invoked as
      yield tornado.gen.Task(twcommon.async.delay, dur)
      """
      delta = datetime.timedelta(seconds=dur)
      return tornado.ioloop.IOLoop.current().add_timeout(delta, callback)
  
subject: Fix comment.