First pass at a set of caching filters and handlers. This implements a

working disk cache.  There are a lot of improvements to be made to this,
but this is a pretty good start to a dynamic cache.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86995 13f79535-47bb-0310-9956-ffa450edef68