Provide easy way to determine indexes needed by Rest2ldap queries

Rest2ldap is being extended with cool features like recursive references and reverse references.

As the set of LDAP searches that Rest2ldap generates to respond to an HTTP request gets larger and less obvious from the pure REST view of the operations, it would be nice to be able to see why searches go unindexed, and give the directory administrator information that allows them to add the necessary indexes.

Today it's possible to disable suppression of access log messages for internal operations, and then try to repeat the LDAP searches with debugsearchindex to determine what might be missing. But it's not easy to do.