'collapsed' class should be added to all triggers, not just the one that initiates the collapse

Created by: jkallay1

When an element is collapsed, the 'collapsed' class should be added to all collapse triggers for that element, not just the one that triggered the collapse. An example use case is where one trigger is used for showing, the other for hiding.

Test case is here. http://jsfiddle.net/G8kRu/5/