On the 2.4.x branch: merge r1778630,1779459,1779525,1779528,1779738 from trunk

On the 2.4.x branch: merge r1778630,1779459,1779525,1779528,1779738 from trunk

  *) mod_http2: rework of stream resource cleanup to avoid a crash in a close
     of a lingering connection. Prohibit special file bucket beaming for
     shared buckets. Files sent in stream output now use the stream pool
     as read buffer, reducing memory footprint of connections.
     [Yann Ylavic, Stefan Eissing]

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1779742 13f79535-47bb-0310-9956-ffa450edef68