Backport trunk changes as recorded in branches/proxy-reqbody-2.0.x,
  refactoring http_proxy.c request body handling.  This correction
  satisfies the vetoed issues in the originally backported proxy
  request body handling from trunk/ in 171205.

Reviewed by: jim, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@290517 13f79535-47bb-0310-9956-ffa450edef68