Backport the corrected C-L streamed, v.s. spooled, v.s. T-E: chunked
  selection logic from httpd trunk/.  This now correctly chooses the
  most portable mechanism (e.g. C-L) when we can see the entire body,
  even for chunked bodies from the client, falls back on spool cl when
  it's necessary, and uses chunked when we have faith in it.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/proxy-reqbody-2.0.x@230728 13f79535-47bb-0310-9956-ffa450edef68