s4:dsdb: split extended_dn into extended_dn_in, extended_dn_out and extended_dn_store.

s4:dsdb: split extended_dn into extended_dn_in, extended_dn_out and extended_dn_store.

By splitting the module, the extended_dn_in and extended_dn_store
moudles can use extended_dn_out to actually get the extended DN.  This
avoids code duplication.

The extended_dn_out module also contains a client implementation of
the OpenLDAP dereference control (draft-masarati-ldap-deref-00).

This also introduces a new control
'DSDB_CONTROL_DN_STORAGE_FORMAT_OID' to ask the extended_dn_out module
to return whatever the 'storage format' is.  This allows us to work
with both OpenLDAP (which performs a dereference at run time) and LDB
(which stores the GUID and SID on disk).

Signed-off-by: Stefan Metzmacher <metze@samba.org>