Merge r572937, r574485, r574486 from trunk:

Be proactively safe. A cheap check, but helps prevents badness :)


* Do not reset lbstatus, lbfactor and lbset if the shared proxy_worker_stat
  structure for a worker is already initialized by the same or another
  process.


* This check is now part of the PROXY_WORKER_IS_INITIALIZED macro.

Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@575709 13f79535-47bb-0310-9956-ffa450edef68