Backport r1306409 from trunk:

* Add the forcerecovery balancer parameter that determines if recovery for
  balancer workers without considering the retry value of workers is enforced.
  There might be cases where an already overloaded backend can get into deeper
  trouble if the recovery of all workers is enforced without considering the
  retry parameter of each worker

Submitted by: rpluem
Reviewed by: rpluem, sf, rjung



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1373320 13f79535-47bb-0310-9956-ffa450edef68