Remove useless and costly StringConcat object.
Avoid some array accesses. 5% of CPU time was wasted there.
Deactivate VSync
Fix comments
Solving merge conflicts
Build the static tiles surface only once on software side.

Now Surface::render() is called ten times less often.
Update the texture if any when drawing on a software destination.
Copy to hardware surface at rendering time
Fix is_rendered usage
Deactivate VSync
Reindent.
Call SDL_UpdateTexture only for software destination surfaces.
Use the more usual RGBA pixel format for colors.

This should speed up fill_with_color() since no conversion is necessary.
Only accelerate the texture when rendering
Merge branch 'texture' of https://github.com/christopho/solarus into texture
Disable assertions on the bottleneck path in release mode.
Merge branch 'master' into texture
Document surface:set_transparency() removal in the changelog.
Forgot to set texture as NULL
More optimizations of assertions in Savegame.