Return the proper status and headers when serving a revalidated response.

* modules/cache/mod_cache.c
  (cache_save_filter): Load in the cached status and headers; send a flush
  rather than an EOS when the client request is conditional.
* modules/cache/mod_cache.h: Export ap_cache_accept_headers.
* modules/cache/cache_storage.c: Rename accept_headers to
  ap_cache_accept_headers.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@152680 13f79535-47bb-0310-9956-ffa450edef68