Rudder

I think the problem is that we have two async command that don't compose well (we don't have a "finish" notification):

- if we start group update without firing "regenerate", we may miss some cases (one ? when group are all empty, or if there is no dyngroups) where the regeneration is not done but should be,
- if we start group update and fire regenerate, we are in the same situation as now, but with an automatic double generation.

Writting that, it seems that letting the group update do the regeneration is better. But then, we have several kind of import, and so we also have to treat differently imports with group from other. So we have some more heuristic to put in place.