Note: SDL_Init is mandatory oterwise SDL_OpenAudio will redo the init.
So the only sane way is to initialize pulseaudio, close everything, and finally
init the requested driver.
V2:
* ifdef SDL2 code
V3:
* use std::string for m_api (avoid issue issue with wx2.8)
* call the good function to properly close subsystem avoid crashes
Gregory Hainaut
2a68c3585c