Discussion: about FlowRuleException

Curently, there seems to be no way for stage 3 to know whether the exception will be granted to a new session created at stage2, or an existing session.

The point is that, when the stage 3 form is valid, and a POST is done without creating a new access rule and a new grading rule, the message is always "Exception granted to XXX in course XXX", however, there's actually no `FlowRuleException` created in the process.

If the above process is for an exising session, that message is kind of misleading (though I know this is a rare case). If the process is for a new session created in stage 2, the message is correct, but there's no way to track which sessions are created throught this exception granting process, if the stage 3 was post (or even bypassed) without creating new access/grading rules.

Start by tracing the stage 2 and stage 3 session flow around FlowRuleException, including the stage 3 form POST when no access or grading rule is created. Determine how existing and newly created sessions are distinguished, then define completion as accurate messaging and a way to identify sessions created through the exception-granting process.

Written by the indexing model from the issue text.