Merge r325960 from trunk:

* Create new filters CACHE_OUT_SUBREQ / CACHE_SAVE_SUBREQ which only differ
  by the type (AP_FTYPE_CONTENT_SET-1) from CACHE_OUT / CACHE_SAVE
  (AP_FTYPE_CONTENT_SET+1). This ensures that subrequests to non local
  resources do not get stuck in the middle of the road with the contents
  only written to the temp file, because CACHE_OUT_SUBREQ / CACHE_SAVE_SUBREQ
  are inserted *before* the SUBREQ_CORE filter in the filter chain.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@328466 13f79535-47bb-0310-9956-ffa450edef68