def clean_url(url, force_scheme=None):
    """Cleans the given URL."""
    # URL should be ASCII according to RFC 3986
    url = str(url)
    # Collapse ../../ and related
    url_parts = urlparse.urlparse(url)
    path_parts = []
    for part in url_parts.path.split('/'):
        if part == '.':
            continue
        elif part == '..':
            if path_parts:
                path_parts.pop()
        else:
            path_parts.append(part)

    url_parts = list(url_parts)
    if force_scheme:
        url_parts[0] = force_scheme
    url_parts[2] = '/'.join(path_parts)

    if FLAGS.keep_query_string == False:
        url_parts[4] = ''    # No query string

    url_parts[5] = ''    # No path

    # Always have a trailing slash
    if not url_parts[2]:
        url_parts[2] = '/'

    return urlparse.urlunparse(url_parts)
Cleans the given URL.