Merge r1836381, r1836382, r1836383, r1836386, r1836603 from trunk:
* mod_proxy: Remove load order and link dependency between mod_lbmethod_* modules and mod_proxy by providing mod_proxy's ap_proxy_balancer_get_best_worker as an optional function.
* Remove invalid copy and paste comments
* Always retrieve conditional function. static variable might contain garbage if module was reloaded in a static build.
* Add missing log numbers
* 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.