Introduce a dedicated cache hash adt that does not rely on pools. This

cures a storage leak when garbage collecting expired entries out of the
hash table. cache_hash is just apr_hash with some of the function removed
and reimplemented to use malloc/free in place of apr_pool calls.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94932 13f79535-47bb-0310-9956-ffa450edef68