Created by: lw
Fixes #9406 (closed).
This fiddle shows the issue with the v3 CSS before my fix (note that the border on the corners isn't rounded, and when hovering the button on the right the "shared edge" doesn't get darker): http://jsfiddle.net/MgcDU/6647/
This is the same fiddle with the new CSS (both issues disappeared): http://jsfiddle.net/MgcDU/6648/
The only change was setting border-collapse: separate on .btn-group-justified, to avoid it inheriting the border-collapse: collapse of the .table it's placed inside.