message: EventIndex: Better logging on how many events are added.
  This adds a bit more info to how many events are added, how many skipped
  and if they are skipped because they are undecryptable.
diff: @@ -469,6 +469,9 @@ export default class EventIndex extends EventEmitter {
  // decryption keys, do we want to retry this checkpoint at a later
  // stage?
  const filteredEvents = matrixEvents.filter(this.isValidEvent);
  + const undecryptableEvents = matrixEvents.filter((ev) => {
  + return ev.isDecryptionFailure();
  + });
  // Collect the redaction events so we can delete the redacted events
  // from the index.
  @@ -503,7 +506,10 @@ export default class EventIndex extends EventEmitter {
  console.log(
  "EventIndex: Crawled room",
  client.getRoom(checkpoint.roomId).name,
  - "and fetched", events.length, "events.",
  + "and fetched total", matrixEvents.length, "events of which",
  + events.length, "are being added,", redactionEvents.length,
  + "are redacted,", matrixEvents.length - events.length,
  + "are being skipped, undecryptable", undecryptableEvents.length
  );
  try {
  