def buildStarted(builderName, build):
    """Builder 'builderName' has just started a build. The build is an
        object which implements IBuildStatus, and can be queried for more
        information.

        This method may return an IStatusReceiver (it could even return
        'self'). If it does so, stepStarted and stepFinished methods will be
        invoked on the object for the steps of this one build. This is a
        convenient way to subscribe to all build steps without missing any.
        This receiver will automatically be unsubscribed when the build
        finishes.

        It can also return a tuple of (IStatusReceiver, interval), in which
        case buildETAUpdate messages are sent ever 'interval' seconds, in
        addition to the stepStarted and stepFinished messages."""
