backport this fix from 2.1-dev:

  proxy HTTP: Rework the handling of request bodies to handle
  chunked input and input filters which modify content length, and
  avoid spooling arbitrary-sized request bodies in memory.

PR:            15859
Reviewed by:   jerenkrantz, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@171205 13f79535-47bb-0310-9956-ffa450edef68