AssertionError: Don't try to render this page when the user is logged in.

To reproduce:

<salgado> 1. log out of LP
<salgado> 2. start logging in in one tab, but stop on login.lp.net/+openid
<salgado> 3. start (and complete) login in another tab
<salgado> 4. go back to first tab and click 'Not now' (or similar)

Another way to reproduce is to do as above but leave the first tab open for 10 minutes or more and then try to complete the authentication there. The authentication will fail because the nonce is expired but the user is already logged in so the login-error page OOPSes.

After discussing this with Gary, when we reach the code path that renders the login-error page and the user is already logged in, we'll just add a notification to the request (stating that the authentication failed but the user is already logged in) and redirect the user to the starting_url included in the OpenID response.

If, for any reason, that's not trivial to do then we'll change the login-error page to display the text that would go in the notification and provide a link to starting_url, when the user is logged in.