title: "takeWhile is not a function" while using with IntervalObservable
body: <p>I have this simple setup in my Angular 2 code:</p>
  
  <pre><code>IntervalObservable.create(5000)
    .takeWhile(() =&gt; this.spinnerOn) // only fires when component is alive
    .subscribe(() =&gt; {
      this.httpService.pollResults()
        .subscribe(data =&gt; {
          console.log(data);
        });
    });
  </code></pre>
  
  <p>The code compiles, and i can see the takeWhile.d.ts used from rxjs node module in my IDE (IDEA). But when the app runs, i see this error in the console: </p>
  
  <pre><code>ERROR TypeError: __WEBPACK_IMPORTED_MODULE_3_rxjs_observable_IntervalObservable__.a.create(...).takeWhile is not a function
  </code></pre>
  
  <p>What am i doing wrong?</p>