Release 0.85 - Oops, caching bug

This is a quick for the previous release, which happened to cache the layer stack too much. You wouldn't see the difference immediately if you chose a different blending mode (you'd have to do something else like paint or change layer then cause a render to see the change). My bad. Oops, it's 2:51 am and I should be sleeping now since tomorrow I am supposed to be in perfect condition at work.