python-openid RP fails without warning when date time is wrong

[shohel02]

In one of our test setup, the system time was backward from the actual time. Due to this reason, python-openid RP library fails in the final stage authentication, even though OP sends success message, without giving any warning or reason for failure. This makes hard to detect the reason of failure. It would be good to have a warning log message when RP fails for this reason.