Implement 'net groupmap set' and 'net groupmap cleanup'.

Implement 'net groupmap set' and 'net groupmap cleanup'.

I was rather annoyed by the net groupmap syntax, I could never get it
right.

net groupmap set "domain admins" domadm

creates a mapping,

net groupmap set "domain admins" -C "Comment" -N "newntname"

should also do what you expect. I'd like to have some feedback on the usability
of this.

net groupmap cleanup

solves a problem I've had two times now: Our SID changed, and a user's primary
group was mapped to a SID that is not ours. net groupmap cleanup removes all
mappings that are not from our domain sid.

Volker