[Users] new group feature

Hi, I have implemented a new group feature. So far we have group support with fixed matching: user X belongs to group G, etc.. This proves to be inefficient when you have huge block of users belonging to small numbers of groups. So I did some regular expression based groups: if user@domain matched a RE -> belongs to group G very usefull if try to provisions routing logic based on groups. I developed this new functionality inside the group module since there is about same functionality and it's too small to be a separate module. any pro or against comments / suggestions before committing? regards, Bogdan