Merge r617822, r627097, r660207 from trunk:

* Do not retry a request in the case that we either failed to sent a part of the
  request body or if the request is not idempotent.

PR: 44334


* As per niq's comment, better destinct the types of idempotence.


* Introduce a flag to decide whether we sent an body to the backend or not.

Submitted by: rpluem
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@660580 13f79535-47bb-0310-9956-ffa450edef68