Merge r692567, r693564, r693577 from trunk:

PR 45687: Detect and pass along error buckets
Submitted by: Dan Poirier <poirier pobox.org>
Reviewed by:  trawick

* stash the brigade used by send_bucket_downstream in the filter context for
reuse.
Submitted by: Dan Poirier <poirier pobox.com>
Reviewed by: gregames, covener

* Use send_bucket_downstream to send data down the chain instead of creating
  a brigade each time.
Submitted by: Dan Poirier <poirier pobox.com>
Reviewed by: rpluem




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@695234 13f79535-47bb-0310-9956-ffa450edef68