Added dummy glXCreateWindow/glXDestroyWindow stubs

Just like glXCreateGLXPixmap/glXDestroyGLXPixmap they don't do
anything useful (and hence are not really correct). Still they are
needed for compiling supertuxkart 0.8 and avoid linking problems:

    undefined reference to `glXCreateWindow'
    undefined reference to `glXDestroyWindow'
Initial fix to add support for 24bpp desktop color depth
Merge branch 'master' of ../glshim-ssvb into HEAD

Conflicts:
	src/glx/glx.c
	src/glx/glx.h
fix small bug where existing display should be used
Merge branch 'ssvb'
don't allow raster data to write outside buffer
enhance glx routines