Propose load balancer enhancements from trunk for backport.

These are:

   o Hot Standby
   o Cluster set
   o balancer_manager additional info
   o docs updates for above




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@437689 13f79535-47bb-0310-9956-ffa450edef68