def user_for_message(message)
      if user = users[message.user_id]
        yield message, user
      else
        message.user do |user|
          yield message, user
        end
      end
    end
def user_for_message(message)
      if user = users[message.user_id]
        yield message, user
      else
        message.user do |user|
          yield message, user
        end
      end
    end
Retrieve the user from a message, either by finding it in the current
 list of known users, or by asking campfire for the user.

 message - the message for which to look up the user

 Yields the message and the user associated with the message