Merge r407357, r408154, r408729 from trunk:

Merge r407357, r408154, r408729 from trunk:

* Handle the cases "no proxy request" and "reverse proxy request" in the same
  manner, when setting scheme and port_str. This is needed because if a cached
  entry is looked up by mod_cache's quick handler r->proxyreq
  is still unset in the reverse proxy case as it only gets set in the
  translate name hook (either by ProxyPass or mod_rewrite) which is run
  after the quick handler hook. This is different to the forward proxy
  case where it gets set before the quick handler is run (in the
  post_read_request hook).
  If a cache entry is created by the CACHE_SAVE filter we always have
  r->proxyreq set correctly.
  Also set scheme to ap_http_scheme(r) instead of "http" to handle SSL
  correctly.

* Fix const compiler warning introduced by r407357.
Noticed by: Joe Orton

* Cleanup the code by replacing some inline code to lower-case a string with
  ap_str_tolower.
Proposed by: Joe Orton

PR: 39593
Submitted by: rpluem
Reviewed by: rpluem, jim, pquerna

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@425035 13f79535-47bb-0310-9956-ffa450edef68