Finish up the header brigades up-front; we simply know ahead of time if
  they are necessary or not.  This changes one behavior; the stream_chunked
  now always sends a transfer encoded body; even if it's nothing but an
  empty body.

  Also, Fix a bugglet in backporting the input_brigade argument; need the
  bucket_alloc already.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/proxy-reqbody-2.0.x@230716 13f79535-47bb-0310-9956-ffa450edef68