title: How to add mod_proxy_wstunnel to Apache2 2.2 on Raspberry Pi (Backport mod_proxy_wstunnel)
body: <p>Raspberry Pi is still on Apache 2.2 (2.2.22-13+deb7u4 right now).
  To use Apache as Proxy for Websockets ("ProxyPass") Apache Module mod_proxy_wstunnel is required.</p>
  
  <p>Apache Module mod_proxy_wstunnel is available in httpd 2.4.5 and later.</p>
  
  <p>How can I add mod_proxy_wstunnel to Apache2 2.2 on Raspberry Pi (Backport mod_proxy_wstunnel)?</p>