Performance fix for prep_walk_cache():

Moved the directory/location/file-walk caches from the
request's pool userdata hash table to the core_request_config
struct.

This change removes about 60% of the processing time from
prep_walk_cache().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92684 13f79535-47bb-0310-9956-ffa450edef68