Implement the util_ldap_cache_getuserdn() API so that the ldap authorization...

Implement the util_ldap_cache_getuserdn() API so that the ldap authorization only modules have access to the util_ldap user cache without having to require ldap authentication as well.  [PR 31898]

Submitted by: Jari Ahonen [jah progress.com]
Reviewed by: bnicholes, wrowe, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@105744 13f79535-47bb-0310-9956-ffa450edef68