Try to fix install failure for xapian on 3.11-dev and newer. distutils.sysconfig.get_config_vars('SO') is returning None on these platforms. Use: sysconfig.get_config_vars('SO') instead. This works with my 3.6 install, so hopefully will work with all of the 3.x releases we have.

try:
    # Python 3+.
    from xmlrpc import client, server
    server.SimpleXMLRPCDispatcher
except (ImportError, AttributeError):
    # Python 2.
    import xmlrpclib as client  # noqa: F401
    import SimpleXMLRPCServer as server