better s-maxage support

 
+  *) mod_cache: Consider Cache-Control: s-maxage in expiration
+     calculations.  [Eric Covener]
+
+  *) mod_cache: Allow caching of responses with an Expires header
+     in the past that also has Cache-Control: max-age or s-maxage.
+     PR55156. [Eric Covener]




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1726675 13f79535-47bb-0310-9956-ffa450edef68