This is the start of a bit of a rewrite of winbindd's connection handling.

This is the start of a bit of a rewrite of winbindd's connection handling.
I've wrapped up all the decisions about managing, making and closing
connections into a connection manager in nsswitch/winbindd_cm.c.

It's rather incomplete at the moment - only querying basic user info works
at the moment (i.e finger -m DOMAIN/user) and everything else is broken.

Jeremy, please take a look and I'll start moving across the rest of
winbindd to this new system.
(This used to be commit c369cf5af787ed9c642778d21f162716fbf0620e)