* bucket resolution is now set from the brush size so there is around 9 buckets under the brush - (previously was fixed to 128x128). * brush sizes below 40 disable multithreading, since threads only speeds up cases where each bucket has enough pixels in it for each core to spend some time. * make smear use bicubic pixel lookups so a low Spacing value works as expected. * smear tool was darkening pixels a tiny bit. * fix for simple mistake causing ProjectPaintImage arrays not to be thread safe.