todo

OpenLdap是LDAP的开源项目

1) must add alias handling
2) [sizelimit moved to frontend]
  must set time limit when preparing all queries, and check size limit
3) there was expressed a need to have access to IP in while constructing
  queries, to have response alter in accordance to client IP. Will add
  preprocessor for values in metatables, which would substitute things
  like "$IP$".
4) must handle NOT filters (see ITS#2652)
5) must map attribute types and syntaxes between LDAP and SQL types (e.g.
  use BLOBs for octet streams)
6) must define another mech to add auxiliary objectClass to all entries
  according to ldap_at_mappings (ldap_entry_objclasses has limitations)