User role nesting

Ahoy,

It would be very helpful if admins could nest groups. When creating a new role, you could choose to nest it within a second role, so that every user in the second role automatically gains access to the new role.

My use case involves the node_privacy_byrole module.We have three roles at the moment:

- marketing_team
- marketing_segmentation_editors
- promo_team

Users with the marketing_team role should automatically gain access to the other two roles. Currently we
then have to add *all three roles to a node's ACL* to ensure they have access to all the content. But that quickly becomes messy, especially as the number of roles and nodes increases. So it's not so much a necessary feature as one that would make administering lots of roles and content with node_privacy_byrole much smoother.