message: Trigger invalidation of caches on mention set
diff: @@ -735,6 +735,10 @@ MatrixHandler.prototype._onAdminMessage = Promise.coroutine(function*(req, event
  }
  features[featureFlag] = args[1].toLowerCase() === "true";
  yield this.ircBridge.getStore().storeUserFeatures(event.user_id, features);
  + if (featureFlag === "mentions") {
  + // We should invalidate caching for this user's channels.
  + this.ircBridge.ircHandler.invalidateCachingForUserId(event.user_id);
  + }
  let notice = new MatrixAction("notice",
  `Set ${featureFlag} to ${features[featureFlag]}`
  );
  