[rt-users] Members handling

[Emmanuel Lacour]

I just figured out that whan a group A is a member of another group B, in
group B, we can see all people of group A as member (fine), but with an
unusefull checkbox as when you try to remove one of those Users member,
it only say that this user is not a member of group B :(

I don't know if it's easy to do (doesn't seems), but it would be nice to
disable those checkbox for 'indirect'  members users or to display a
more convenient information message.