* ap_proxy_balancer_get_best_worker cannot be exported and used as an optional

  function at the same time. So rename ap_proxy_balancer_get_best_worker to
  proxy_balancer_get_best_worker and make it static which is then used as an
  optional function and recreate ap_proxy_balancer_get_best_worker as an
  exported thin wrapper of proxy_balancer_get_best_worker.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1836603 13f79535-47bb-0310-9956-ffa450edef68