r3566: Completely replace the queryuseraliases call. The previous implementation...

r3566: Completely replace the queryuseraliases call. The previous implementation does
not exactly match what you would expect.

XP workstations during login actually do this, so we should better become a
bit more correct. The LDAP query issued is not really fully optimal, but it is
a lot faster and more correct than what was there before. The change in
passdb.h makes it possible that queryuseraliases is done with a single ldap
query.

Volker
(This used to be commit 2508d4ed1e16c268fc9f3676b0c6a122e070f93d)