Merge r1597533, r1649491, r1665216, r1756553, r1756631, r1726675, r1718496, r1718476, r1747469 from trunk:

mod_cache: try to use the key of a possible open but stale cache entry
if we have one in cache_try_lock(). PR 50317

Submitted by: Ruediger Pluem


* modules/cache/mod_socache_memcache.c (socache_mc_store): Pass
  through expiration time.

Submitted by: Faidon Liambotis <paravoid debian.org>, jorton


* mod_cache: Preserve the Content-Type in case of 304 response.
304 does not contain Content-Type and mod_mime regenerates
the Content-Type based on the r->filename. This later leads to original
Content-Type to be lost (overwriten by whatever mod_mime generates).


mod_cache: Use the actual URI path and query-string for identifying the
cached entity (key), such that rewrites are taken into account when
running afterwards (CacheQuickHandler off).  PR 21935.
 


mod_cache: follow up to r1756553: log the real/actual cached URI (debug).



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]




remove dead code leftover from r1023387. 

Prior to this revision, there was an apr_atoi64 in this context.
Now, ap_cache_control() sets control.max_age (which is checked here) when
the maxage value was parsed OK.



duplicate debug-level AH00764 in the just-validated path.



Rename ap_casecmpstr[n]() to ap_cstr_casecmp[n](), update with APR doxygen
Submitted by: jkaluza, jorton, jkaluza, ylavic, ylavic, covener, covener, covener, wrowe
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1772331 13f79535-47bb-0310-9956-ffa450edef68