url: fix UnicodeDecodeError on certificate verification error
SSLSocket.getpeercert() returns tuple containing unicode for 'subject'.
Since Mercurial does't support IDN at all, it just returns error for non-ascii
certname.
To run the tests, do:cd tests/python run-tests.pySee http://mercurial.selenic.com/wiki/WritingTests formore information on writing tests.