Make logout a bit easier.

First, there’s no reason to obtain the logout URLs only when logout was initiated. If we get them always, we allow templates to do fancy things like using javascript to do everything on the fly, without going through the script, by dynamically loading the iframes.

Second, we should always check the associations against the ones registered in the session. That way, we can log SPs out individually, and if we refresh the page after that, they will still be marked as logged out.