code: function() {
          var handle = this.on.apply(this, arguments);
          handle.each(function(hand) {
              if (hand.sub) {
                  hand.sub.once = true;
              }
          });
          return handle;
      }
docs: Listen to a custom event hosted by this object one time.
  This is the equivalent to <code>on</code> except the
  listener is immediatelly detached when it is executed.
  @method once
  @param type    {string}   The type of the event
  @param fn {Function} The callback
  @param context {object} optional execution context.
  @param arg* {mixed} 0..n additional arguments to supply to the subscriber
  @return the event target or a detach handle per 'chain' config