This adds winbind-generated groups showing up in 'getent group'. It is not

This adds winbind-generated groups showing up in 'getent group'. It is not
very efficient though, it only does one group at a time. Needs improving, but
the structures are not particularly easy to set up, so check in the basically
working part for others to review.

I'm close to saying that I would like to remove aliases from general group
mapping. These can not be reflected correctly in /etc/group, winbind could do
a better job here.

And having aliases only on machines with nss_winbind at least for me is not a
too severe limitation.

Comments?

Volker