Make cache_server_conf, cache_enable and cache_disable private. Remove

public prefixes from ap_cache_accept_headers, ap_cache_try_lock and
ap_cache_get_providers.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1000211 13f79535-47bb-0310-9956-ffa450edef68