activateCollapsibles() doesn't play nice with YUI effects; needs to be reimplemented using YUI

[Graham Binns]

At the moment we use a custom activateCollapsibles() function to turn fieldsets with the class "collapsible collapsed" into toggle-able collapsed areas on a page. This function is old and crufty, as mars observed:

 <mars> gmb, I would avoid that function altogether. It's nasty. And incorrect in subtle ways.

Moreover, when used inside an element that gets hidden and shown using Y.lazr.effects.slide_(in|out), nasty things happen (see attached screenshot).

To get around this, we should re-implement activateCollapsibles() using YUI. The functionality should stay the same, except that it can use the slide_in and slide_out animations to make things a bit more pleasing to the eye.

Note that it may be better to write a replacement function to be used in cases where the existing functionality is inadequate before transitioning all collapsibles to use the new code.

[Diogo Matsubara (matsubara)]

Fixed in devel r8818.