Use addQuotes() consistently when building lists of group and user names.

Use addQuotes() consistently when building lists of group and user names.
Some were missing the quoting, using raw strencode(). This caused mysql errors at best, and hypothetically could be used for some kind of sql injection. :)

I'd recommend making further refactoring to use the query-building functions ($db->select, $db->update, etc) to avoid having to do these by hand.