If SDL_OpenAudio() is passed zero for the desired format
fields, the following environment variables will be used
to fill them in:
	SDL_AUDIO_FREQUENCY
	SDL_AUDIO_FORMAT
	SDL_AUDIO_CHANNELS
	SDL_AUDIO_SAMPLES
If an environment variable is not specified, it will be set
to a reasonable default value.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401753