title: does "taken" observables implicitly complete?
body: <p>Having<br>
  <code>obs1 = new Rx.Observable.interval(1000);
  obs2 = obs1.take(2);</code><br>
  <code>obs2</code> will complete after the second value emitted by <code>obs1</code>.<br>
  what about <code>obs1</code> ?<br>
  will it complete as well or will it keep on firing? </p>