Revoking permission to search for users and groups

I've seen a few customers who wish to make their user lists less public. For example CONF-5550 requests the ability to not notify of changes to user profiles.

Another way the user lists are publicised is by the Space Admin -> Permissions page.

This page gives all space administrators (including personal space administrators) the ability to do wildcard searches for users and for groups.

A customer has suggested that there should be global permissions allowing "search for users" and "search for groups" and that space administrators without these permissions can only give permissions to users and groups that they know the names of.