OLPC: Adding a little border around SuperTux

Still haven't looked deeper into the issue of how to change the resolution on the OLPC, however I did a little experiment with simply adding a border around the screen, the result is this:

• 7019392d02f7e04a3060ccf85265e05e-supertux-olpc.png

Looks for most part quite nice (just a placeholder of course) and raised the idea to have SuperTux run at different screensizes, have worldmap, menu and such run at fullscreen, while running the game with a smaller window size. Whatever will be implemented in the end, SuperTux already is quite playable as it is. This patch also makes SuperTux run in a window instead of fullscreen, so all the brightness controls and such work as normal on the OLPC.

Patch to get the above result is available on request, likely I'll open a new branch in SuperTux SVN in the next days.

Some other issues the game currently has:

• tearing is currently rather obvious and annoying
• the game doesn't have fixed size steps, so if the computer gets busy with other stuff it makes large jumps, often deadly for Tux
• calling the sugar frame and similar adjustments sometimes doesn't work properly
• alpha-blending, it is likely worth it to get rid of any of that to get faster fps