(Session Information): Added Scheduling-Info.

(Protocol Requests): Changed the status of set-keep-commented from
	experimental to recommended.
(get-stats-description): State that this always returns the same
	during a session, so clients can cache this value aggressively.
(get-stats): Elaborate on the access-denied error code.
(get-scheduling): New request.
(set-scheduling): New request.
(Error Codes): Added priority-denied, weight-denied and weight-zero.