Corrected privilege-related problems. Many functions now
        take a Connection instead of a Pers_no/Person combo.

        Added defensive code to protect the server in situations
        where active_connection is unexpectedly NULL.

        Added checks to most RPC handlers to make sure they are only
        called when there is an active connection.

        The added_by field for a person's membership in its letterbox
        conference is not the person itself, not 0.

Testing
        Removed all new expected fails from the testsuite.