Merge r1899451, r1899454, r1899562, r1899564, r1899584, r1899886 from trunk:

Merge r1899451, r1899454, r1899562, r1899564, r1899584, r1899886 from trunk:

* Close the connection in case an EOC bucket was seen

* In case we see an EOC bucket and there was an error bucket before, use its
  status as status for the request. This should ensure proper status logging
  in the access log.

* We need to set r->status on each call after we noticed an EOC as
  data bucket generators like ap_die might have changed the status
  code. But we know better in this case and insist on the status
  code that we have seen in the error bucket.

* Keep track of the number of keepalives we processed on this connection.

* Report a broken backend in case reading the response line failed on the
  first request on this connection otherwise we assume we have just run
  into a keepalive race and the backend is still healthy.

* Add Changelog for r1899451, r1899454, r1899562, r1899564, r1899584

Submitted by: rpluem
Reviewed by: jim

Github: closes #314

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1900755 13f79535-47bb-0310-9956-ffa450edef68