- introduce macros for 3 directories, replacing expanded references
        throughout: %%{pylibdir}, %%{dynload_dir}, %%{site_packages}
    - explicitly list all lib-dynload files, rather than dynamically gathering
        the payload into a temporary text file, so that we can be sure what we
        are shipping; remove now-redundant testing for presence of certain .so
        files
    - remove embedded copy of zlib from source tree before building