o Minor features:

    - Log (at debug level) whenever a circuit's purpose is changed.

    - Allow controllers to request an event notification whenever a
      circuit is cannibalized or its purpose is changed.  Implements
      part of ticket 3457.

    - Include the creation time of a circuit in CIRC and CIRC2
      control-port events and the list produced by the 'GETINFO
      circuit-status' control-port command.