[adv_windowlist] sort in order of first activity

It would be cool if the AWL could be sorted in order of activity *first* occuring, i.e. the item on the left end would be the one that had activity before all the others, while an item that receives activity for the first time would be appended to the right.

Or vice versa, with '-' prepended…

I stared at the code for a while but couldn't figure it out. If you have any clues, then I could also just give it a try.