(merge from 3.0)

(merge from 3.0)

Change our Domain controller lookup routines to more carefully seperate
DNS names (realms) from NetBIOS domain names.

Until now, we would experience delays as we broadcast lookups for DNS names
onto the local network segments.

Now if DNS comes back negative, we fall straight back to looking up the
short name.

Andrew Bartlett
(This used to be commit 4c3bd0a99e464198d243da302ff1868189b4dcff)