Merge r1206286 from trunk:

Move useful and shared balancer stuff to the shm slot...
Provide hooks for post-config/runtime addition of
balancers.
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1206287 13f79535-47bb-0310-9956-ffa450edef68