object -- because we just care about one event we can simply use a
threading.Event object.  Specific changes include,

BerkeleyBase.py

    __init__(): Simplify the creation of the checkpointer and
    autopacker worker threads.

    close(): Replace autopacker.stop() with setting the Event object.
    This both kicks us out of the wait() and sets the thread's
    internal stop flag, so it's all we need.

    _WorkThread.init(): Take the `name' argument out of the
    constructor.  It was the only thing that 2/3rds of the subclasses
    needed to override, so just stick it in a class attribute.

    run(): Simplify to use the Event object.  Also, change _nextcheck
    to recalculate `now' after the work is done.  There's no telling
    how much time the work will take (it may not matter much in
    practice).

    stop(): Removed.

    _Checkpoint.__init__(): Removed

Full.py

    _make_autopacker(): Updated

    _Autopack.__init__(): Updated

Minimal.py

    _make_autopacker(): Updated

    _Autopack.__init__(): Removed