Fix the OSX build and make it easier

There is one remaining bug.

Fullscreen modes which are buggy on OSX 10.7 and +, and with Solarus 0.9.3. With the 1.X branch, fullscreen modes are not even selectable. I guess the cause is something like VideoManager:is_mode_valide().

The point is, should I debug/optimize properly on 1.X branch and possibly revert some commits and add temporary code, or wait for the SDL2.0 release and then still use the "intermediate surface" workaround on 0.9 branch for now ?