There was a lot of gp2x-specific code which was built for
all platform. For instance, the code was compiled for all
the platforms with the constant "TARGET_GP2X" defined.
This obviously had to be fixed.
Instead of having the copy constructor convert to display format, the new
copy constructor preserves the pixel format and a separate method was
introduced to convert surfaces to display format.
The code was made more robust as well: it should no longer crash if the
wallpaper cannot be loaded.