Rendering proper boxfilter rescales at full resolution takes a lot more
effort per frame than nearest neighbor.

After this change the default behaviro with the idle and thread renderers is to
render queued redraws with nearest neighbor interpolation - possibly reusing a
cache that otherwise is correct containing higher quality cached resized blit.
After more than 333ms have passed since the last queued draw, and the cache is
containing nearest neighbor interpolated contents, queue a redraw with full
quality.

This change replaces the earlier tweak that during playback we only use
nearest neighbor interpolation, during video or animation playback the
frequency of queued redraws means we never end up queuing a full quality
redraw.