[WIP] Implement buffer damage and scaling

Created by: acrisci

It's sort of difficult to test this right now and the work I will do next might reveal some errors, but I think it is ok.

Try ./weston-simple-damage --scale=2 and compare it to ./weston-simple-damage --scale=2 --use-damage-buffer. You'll notice that they both do not work now and I think that is the correct behavior. What I tested is that the damage rects are in the same coordinate system after they are applied (e.g., the damage box height/width is ~21 for every value you give to scale). I believe this is what is meant by converting buffer coordinates to surface coordinates.

Buffer scaling should not affect the size of the window presented on the screen. Try different scales in weston and you will see what I mean. Once that is fixed, we should see the little green ball move around with scale. That will be what I work on next.