Add CacheStorePrivate, CacheStoreNoStore, and clarify CacheIgnoreCacheControl.

* docs/manual/mod/mod_cache.xml: Update documentation for
  CacheIgnoreCacheControl and add documentation for two new directives.
* modules/cache/mod_cache.c
  (cache_url_handler): Honor 'Cache-Control: no-cache' request header.
  (cache_save_filter): Only honor no-store or private when their respective
                       directives are Off (which is the default).
  rest of file: add in standard configuration syntax stuff...
* modules/cache/mod_cache.h: Minor formatting tweak and add new fields.

Suggested by: Pier Fumagalli


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@149492 13f79535-47bb-0310-9956-ffa450edef68