I've posted a quick fix for the tiny next turn button. The change is marked as "stable", which means that everyone should download it automatically when they start the game.
The new button isn't quite as fancy as the one in Arioch's latest UI concepts (which should theoretically change colors and glow and so on in response to the actions you've taken during a given turn), but, it's certainly an improvement on the original.
I've also rearranged some of the other image files -- a little housekeeping that will have the effect of making the patch download bigger than it really needs to be. Consider that a test of the updater's bookkeeping abilities