def interrupt():
    """This is called to tell the Command that the build is being stopped
        and therefore the command should be terminated as quickly as
        possible. The command may continue to send status updates, up to and
        including an 'rc' end-of-command update (which should indicate an
        error condition). The Command's deferred should still be fired when
        the command has finally completed.

        If the build is being stopped because the worker it shutting down or
        because the connection to the buildmaster has been lost, the status
        updates will simply be discarded. The Command does not need to be
        aware of this.

        Child shell processes should be killed. Simple ShellCommand classes
        can just insert a header line indicating that the process will be
        killed, then os.kill() the child."""
