s3-netlogon: enumerate UPN suffixes from PASSDB when available

s3-netlogon: enumerate UPN suffixes from PASSDB when available

Optionally append list of UPN suffixes if PDB module returns non-empty one.

Refactor fill_forest_trust_array() in source3 to allow reuse of the code between
_netr_DsRGetForestTrustInformation() and _netr_GetForestTrustInformation()

Implement a special case of _netr_DsRGetForestTrustInformation in smbd
when trusted_domain_name is NULL (covered by test_DsrEnumerateDomainTrusts()
in rpc.netlogon torture tests, see comment in source4/torture/rpc/netlogon.c).

Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Tue Apr  9 22:19:34 CEST 2013 on sn-devel-104

The last 4 patches address bug #9779 - add UPN enumeration to passdb internal
API.

Autobuild-User(v4-0-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-0-test): Thu Jul 18 21:53:53 CEST 2013 on sn-devel-104