Fix load order dependencies in LDAP code by switching to use of APR

Fix load order dependencies in LDAP code by switching to use of APR
optional functions for the inter-module API:

* modules/ldap/ldap_private.h: New file, containing "real" function
  declarations, copied from...

* include/ap_ldap.h.in, include/ap_ldap_url.h,
  include/ap_ldap_option.h, include/ap_ldap_init.h,
  include/ap_ldap_rebind.h: ... here.  All declarations changed to APR
  optional function declarations.

* modules/ldap/util_ldap.c (util_ldap_register_hooks): Register all
  the new optional functions.

* modules/aaa/mod_authnz_ldap.c (ImportULDAPOptFn): Pick up optional
  function stub for ap_ldap_url_parse.
  (mod_auth_ldap_parse_url): Use it here.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1140069 13f79535-47bb-0310-9956-ffa450edef68