title: Equivalent of MultiThreadedHttpConnectionManager.shutdownAll() in HttpClient 4.x
body: <p>With <code>HttpClient</code> 3.x there was a static <code>MultiThreadedHttpConnectionManager.shutdownAll()</code> which we invoked from a <code>ServletContextListener#contextDestroyed()</code> to clean up all potentially hanging threads (prevent classloader leaks).</p>
  
  <p>With <code>HttpClient</code> 4.x this is gone but there's <code>PoolingClientConnectionManager</code>. However, it's got no static methods to shutdown connections.</p>
  
  <p>How to go about this?</p>