r15543: New implementation of 'net ads join' to be more like Windows XP.

r15543: New implementation of 'net ads join' to be more like Windows XP.
The motivating factor is to not require more privileges for
the user account than Windows does when joining a domain.

The points of interest are

* net_ads_join() uses same rpc mechanisms as net_rpc_join()
* Enable CLDAP queries for filling in the majority of the
  ADS_STRUCT->config information
* Remove ldap_initialized() from sam/idmap_ad.c and
  libads/ldap.c
* Remove some unnecessary fields from ADS_STRUCT
* Manually set the dNSHostName and servicePrincipalName attribute
  using the machine account after the join

Thanks to Guenther and Simo for the review.

Still to do:

* Fix the userAccountControl for DES only systems
* Set the userPrincipalName in order to support things like
  'kinit -k' (although we might be able to just use the sAMAccountName
  instead)
* Re-add support for pre-creating the machine account in
  a specific OU
(This used to be commit 4c4ea7b20f44cd200cef8c7b389d51b72eccc39b)