[JENKINS-14843]

We can't merge the proposed patch as is, and we should switch to POST if that's what has to happen.
In the mean time, at least provide an escape hatch to allow people to bypass the team extension.

Run Jenkins with -Dhudson.plugins.openid.impl.TeamsExtension.disable=true to disable the team extension.
carry forward error code
[JENKINS-9978] Improve the error diagnosis

When YADIS discovery fails, openid4java does not report the URL it is hitting, making error diagnosis difficult.