title: android: cancel(true) does not kill the AsyncTask
body: <p>I am using an Android <code>AsyncTask</code> in order to download files from a server. when files are downloaded, I am trying to kill the AsyncTask. </p>
  
  <pre><code>protected void onPostExecute(Void result) {
      MyTask.cancel(true);
  }
  </code></pre>
  
  <p>But it stills running (I can see it from the Debug window in eclipse).
  How to kill the AsyncTask?</p>