r25092: Add support for storing trusted domain passwords in LDAP for

r25092: Add support for storing trusted domain passwords in LDAP for
passdb backend = ldapsam.

Along with reproducing the functionality of the secrets.tdb
code, I have prepared the handling of the previous trust password
(in case we are contacting a dc which does not yet know of a recent
password change). This information has still to be propagated
to the outside, but this requires a change of the api and also
a change of the secrets.tdb code.

Michael
(This used to be commit 6c3c20e6c4a2b04de8111f2c79b431f0775c2a0f)