"collapsed" class is not added correctly to accordion toggles

Created by: chenghong

This issue can be viewed on the official documentation page for Collapse at http://twitter.github.com/bootstrap/javascript.html#collapse

When I click on an accordian-toggle to expand its body, the "collapsed" class should be applied to all other accordian-toggles within the same accordion, as they will now become collapsed.

Currently, Bootstrap only applies the "collapsed" class to an accordion-toggle element when that element is explicitly clicked on to collapse its expanded body.