This commit adds a test where we trigger a situation which would
previously make the link think it was never in sync, and potentially
create a lot of empty state updates. This would happen if we were
waiting for a revocation, while still receiving updates from the remote.
Since in this case we could not ACK the updates because of the exhausted
revocation window, our local commitchain would extend, while the remote
chain would stall. When we finally got the revocation the local
commitment height would be far larger than the remote, and FullySynced
would return false from that point on.
854e2a0581