Merge r777042, r777091, r778438, r778439 from trunk:

* Add CacheIgnoreURLSessionIdentifiers directive to ignore
  defined session identifiers encoded in the URL when caching.


* Improve documentation for CacheIgnoreURLSessionIdentifiers

Submitted by: Dan Poirier <poirier pobox.com>


* Use the correct constant.


* Correctly detect if CacheIgnoreURLSessionIdentifiers is set.

Submitted by: rpluem
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@808906 13f79535-47bb-0310-9956-ffa450edef68