title: NSURLSession dataTaskForRequest:completion: unrecognized selector sent to instance
body: <p>When trying to create my own session object <code>NSURLSession()</code> and request an url I get an unrecognized selector exception but when I use the shared session <code>NSURLSession.sharedSession()</code> everything works fine. How come?</p>
  
  <pre><code>var url = NSURL(string: "http:/www.google.com")
  if url != nil {
      //throws unrecognized selector when dataTaskWithURL is called
      let session=NSURLSession()
      session.dataTaskWithURL(url!)
  
     //works
      let sharedSession=NSURLSession.sharedSession()
      sharedSession.dataTaskWithURL(url!)
  }
  </code></pre>