s4:dsdb/common: add helper functions for trusted domain objects (tdo)
The most important things is the dsdb_trust_routing_table with the
dsdb_trust_routing_table_load() and dsdb_trust_routing_by_name() functions.
The routing table has knowledge about trusted domains/forests and
enables the dsdb_trust_routing_by_name() function to find the direct trust
that is responsable for the given name.
This will be used in the kdc and later winbindd to handle cross-trust/forest
routing.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>