Created by: Illianthe
Issue: Double borders are being shown when using justified button groups (see examples at http://getbootstrap.com/components/#btn-groups-justified).
This can be resolved by setting border-collapse: collapse on the base class, but I noticed that it was explicitly set in 1e1b5c73 to resolve #9406 (closed).
I've fixed this by removing one of the borders when multiple buttons are present in a group.