Naming of system groups

[Maxwell Kanat-Alexander]

> The thing to watch out for here is people who have customized their 
> Bugzilla using UserInGroup() tests...  this kind of thing needs big bold 
> letters in the release notes if we do it. :)

	Indeed. I would probably suggest that any groups that existed in 2.16
should have the same names as they did, and only groups added to 2.18
should have the underscore added.

	Or, if this change is happening in 2.20, do it for 2.20-added groups.

	Renaming things can cause a lot of pain.

	-Max