canonicalize_url breaks certain url(s)

The url /cmp/Supermercados-Dia%25 is incorrectly unquoted into /cmp/Supermercados-Dia%

Problem happens in 
`def _unquotepath(path):
    for reserved in ('2f', '2F', '3f', '3F'):
        path = path.replace('%' + reserved, '%25' + reserved.upper())
    return urllib.unquote(path)`
