title: error_callback in multiprocessing.Pool apply_async in Python 2?
body: <p>Function <code>apply_async</code> of <code>multiprocessing.Pool</code> class has argument <code>error_callback</code> in <em>Python 3</em>. But this argument is missing in <em>Python 2</em>. </p>
  
  <p>Is there any trick to achieve the same functionality in Python 2 ? Ideally I would like to write code which runs in both Python 2 and 3.</p>