Scene loads and saves

• A scene load releases every claim. After a single-scene load, every claim is released and every value still alive is put back. Take the NPC again from Events.WhenReady if you still need it.
• A Take called straight from an Events.SceneLoaded handler is refused, because the load gate is set for the whole of that event and Take returns false while it is set.
• Saving does not change anything the framework holds. Take is refused while the save runs, and Release still works.