mod_proxy_balancer: Add failontimeout parameter. Timeout will put worker
in error state if an IO timeout is detected.

trunk patch: http://svn.apache.org/viewvc?view=revision&revision=1465839
2.4.x patch: http://people.apache.org/~druggeri/patches/httpd-2.4.x-failontimeout.patch

Submitted by: druggeri
Reviewed by: jim, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1476689 13f79535-47bb-0310-9956-ffa450edef68