Arrange the health_checker: add set_slotmem_storage_method(),

create_slotmem() and attach_slotmem(). Arrange corresponding
files.

Start using the health logic in the balancer.

Arrange ap_proxy_add_worker_to_balancer().



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/httpd-proxy-scoreboard@427623 13f79535-47bb-0310-9956-ffa450edef68