message: return () instead of bool
diff: @@ -34,9 +34,9 @@ impl<ST> MultiVerse<ST> {
  if !self.known_states.contains_key(k) {
  self.known_states.insert(*k, st);
  if self.tips.remove(prevhash) {
  - self.tips.insert(*k)
  + self.tips.insert(*k);
  } else {
  - self.tips.insert(*k)
  + self.tips.insert(*k);
  }
  }
  }
  