schemes: fix // breakage with Python 2.6.5 (issue2111) Recent Pythons (e.g. 2.6.5 and 3.1) introduce a change that causes urlparse.urlunparse(urlparse.urlparse('x://')) to return 'x:' instead of 'x://'i and urlparse.urlunparse(urlparse.urlparse('x:///y')) to return 'x:/y' instead of 'x:///y'. Fix url.hidepassword() and url.removeauth() to handle these cases.