idmap_adex: Add new idmap plugin for support RFC2307 enabled AD forests.

idmap_adex: Add new idmap plugin for support RFC2307 enabled AD forests.

The adex idmap/nss_info plugin is an adapation of the Likewise
Enterprise plugin with support for OU based cells removed
(since the Windows pieces to manage the cells are not available).

This plugin supports

  * The RFC2307 schema for users and groups.
  * Connections to trusted domains
  * Global catalog searches
  * Cross forest trusts
  * User and group aliases

Prerequiste: Add the following attributes to the Partial Attribute
Set in global catalog:

  * uidNumber
  * uid
  * gidNumber

A basic config using the current trunk code would look like

 [global]
      idmap backend = adex
      idmap uid = 10000 - 29999
      idmap gid = 10000 - 29999
      winbind nss info = adex

       winbind normalize names = yes
       winbind refresh tickets = yes
       template homedir = /home/%D/%U
       template shell = /bin/bash
(cherry picked from commit 62785b8e2aa862b7eb85e20a11f7a29e1e8b2825)