Issue #7213 - collapsed class not added correctly to non-clicked divs.

Proof of concept:
[Unmodified Bootstrap](http://brianholt.me/pages/unmodified.html)
[Bootstrap with proposed changes](http://brianholt.me/pages/modified.html)

The collapsed class is not added to the other .accordion-toggle correctly. This makes styling the .accordion-toggle for active and inactive states impossible. Corresponds with Issue #7213.

I was unsure if I should pull this to wip or master, but the documentation says make pull requests to wip where possible. However, I believe that the current master branch should be patched as well.