Initially open collapsable fieldset class in admin

It's just an extension for the admin. Replace the collapse.js (collapse.min.js) and use it like this in the admin fieldset option: ´´**'classes': ['collapse', 'open']**´´. Without the 'open'-class, it will work as usual. *Needs possibly fixing for IE <= 8* because IE doesn't support the ´´:not´´ selector.