I was not sure whether Andrew is still interested. I made a simple-minded patch following his proposal. I also added tests and changed docs accordingly. Note that I also changed the expected MRO for MutableSequence in one of the functools tests according to the new hierarchy (otherwise test_functools fails).

Please review.

PS: Some tests was skipped on my machine, here is the list:
    test_bz2 test_curses test_dbm_gnu test_dbm_ndbm test_devpoll
    test_idle test_kqueue test_lzma test_msilib test_ossaudiodev
    test_smtpnet test_socketserver test_ssl test_startfile test_tcl
    test_timeout test_tix test_tk test_ttk_guionly test_ttk_textonly
    test_urllib2net test_urllibnet test_winreg test_winsound
    test_xmlrpc_net test_zipfile64