Fixed delaying subrequests. Similar to 7fcf209d40c8 in the limit_req module, we now set wev->delayed to avoid interference with other subrequests. With 903fb1ddc07f in nginx (wev->delayed handling moved to the connection event handler, nginx 1.11.13), it will be also possible to remove wev->timedout tests and wev->timedout / wev->delayed reset after the timer expiration. These are preserved for now to make the code compatible with older nginx versions.