2.2.x only.

mod_proxy: Reuse proxy/balancer workers' parameters and scores across
graceful restarts, even if new workers are added, old ones removed, or
the order changes.

Proposed by: jkaluza
Reviewed by: ylavic, jkaluza, wrowe
Backported by: ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1680920 13f79535-47bb-0310-9956-ffa450edef68