message: make sure a thread is joined
diff: @@ -46,7 +46,7 @@ fn check_rwlock_unlock_bug1() {
  // Make a waiting writer.
  let l2 = l.clone();
  - thread::spawn(move || {
  + let t = thread::spawn(move || {
  let mut w = l2.write().unwrap();
  *w += 1;
  });
  @@ -59,6 +59,7 @@ fn check_rwlock_unlock_bug1() {
  thread::yield_now();
  assert_eq!(*r2, 0);
  drop(r2);
  + t.join().unwrap();
  }
  fn check_rwlock_unlock_bug2() {
  