RFC 2616 13.2.1 calls out max-age as being a valid 'explicit expiration time',

so per Sec. 13.9 permit queries with just max-age instead of only Expires.

* modules/cache/mod_cache.c
  (cache_save_filter): Be closer to RFC 2616's intent for query arguments.
* CHANGES: Update.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@538807 13f79535-47bb-0310-9956-ffa450edef68