Changes:

 * Handles non-existent backends and generally deals with failed
backends more responsibly.

 * Checks queue for expired requests more optimally.

 * Adds new nginx.conf configuration option:
     max_connections_queue_timeout (defaults to 1 sec).

 * Use random() for backend selection instead of a rotating index.

 * Add patch for the Nginx 0.6.33 (it was just released)

 * Change Nginx killing in the test script (wasn't working in OSX)