Add support for the _NET_WM_BYPASS_COMPOSITOR hint

This hints to window managers to unredirect the window to improve
performance.
Fixed bug 1976 - SDL2.m4 shares same variables as SDL.m4 so they cache values

Edgar Simo

So basically the issue is that:

AC_PATH_PROG(SDL_CONFIG, sdl2-config, no, [$PATH])

in sdl2.m4 shares the same variable (SDL_CONFIG) as sdl.m4:

AC_PATH_PROG(SDL_CONFIG, sdl-config, no, [$PATH])

What happens is if you run the AM_PATH_SDL2 and then AM_PATH_SDL to say fall back on SDL if SDL2 isn't found, the AM_PATH_PROG command gets cached (ac_cv_path_SDL_CONFIG) so that unless you unset this cache variable, the result for AM_PATH_SDL will be EXACTLY the same as for AM_PATH_SDL2.

To fix I would recommend renaming SDL_CONFIG to SDL2_CONFIG in sdl2.m4, replacing all instances so it won't cache to the same variable.