features.m4: Suggest installing SDL2_mixer instead of SDL_mixer
Currently features.m4 suggests installing SDL_mixer when the sound support is missing.
In S2_6 either SDL_mixer or SDL2_mixer is needed, so I guess SDL_mixer is sort of generic name for both of these and should not be touched.
Later branches need SDL2_mixer, and should say so.
Currently features.m4 suggests installing SDL_mixer when the sound support is missing.
In S2_6 either SDL_mixer or SDL2_mixer is needed, so I guess SDL_mixer is sort of generic name for both of these and should not be touched.
Later branches need SDL2_mixer, and should say so.