Given an Invenio URL returns a tuple with two elements. The first is the
    canonical URL, that is the original URL with CFG_SITE_URL prefix, and
    where the ln= argument stripped. The second element element is mapping,
    language code -> alternate URL

    @param quote_path: if True, the path section of the given C{url}
                       is quoted according to RFC 2396

def get_canonical_and_alternates_urls(
        url,
        drop_ln=True,
        washed_argd=None,
        quote_path=False):
    """
    Given an Invenio URL returns a tuple with two elements. The first is the
    canonical URL, that is the original URL with CFG_SITE_URL prefix, and
    where the ln= argument stripped. The second element element is mapping,
    language code -> alternate URL

    @param quote_path: if True, the path section of the given C{url}
                       is quoted according to RFC 2396
    """
    dummy_scheme, dummy_netloc, path, dummy_params, query, fragment = urlparse(
        url)
    canonical_scheme, canonical_netloc = urlparse(cfg.get('CFG_SITE_URL'))[0:2]
    parsed_query = washed_argd or parse_qsl(query)
    no_ln_parsed_query = [(key, value)
                          for (key, value) in parsed_query if key != 'ln']
    if drop_ln:
        canonical_parsed_query = no_ln_parsed_query
    else:
        canonical_parsed_query = parsed_query
    if quote_path:
        path = urllib.quote(path)
    canonical_query = urlencode(canonical_parsed_query)
    canonical_url = urlunparse(
        (canonical_scheme,
         canonical_netloc,
         path,
         dummy_params,
         canonical_query,
         fragment))
    alternate_urls = {}
    for ln in cfg.get('CFG_SITE_LANGS'):
        alternate_query = urlencode(no_ln_parsed_query + [('ln', ln)])
        alternate_url = urlunparse(
            (canonical_scheme,
             canonical_netloc,
             path,
             dummy_params,
             alternate_query,
             fragment))
        alternate_urls[ln] = alternate_url
    return canonical_url, alternate_urls