Listed six classes that break deepcopy.

    _classes_to_fix = (
        documentationtools.ClassDocumenter,
        lilypondparsertools.LilyPondParser,
        lilypondparsertools.ReducedLyParser,
        lilypondparsertools.SchemeParser,
        quantizationtools.ParallelJobHandlerWorker,
        rhythmtreetools.RhythmTreeParser,
        )

No idea what's going on here. The classes will be skipped in the parameterized
deepcopy tests.