Dealing with hints after a topology change

Hints are stored and delivered by destination node id. This allows them to survive IP changes in the target, while making "scan all the hints for a given destination" an efficient operation. However, we do not detect and handle new node assuming responsibility for the hinted row via bootstrap before it can be delivered.

I think we have to take a performance hit in this case – we need to deliver such a hint to all replicas, since we don't know which is the "new" one. This happens infrequently enough, however – requiring first the target node to be down to create the hint, then the hint owner to be down long enough for the target to both recover and stream to a new node – that this should be okay.