Fix SIGTERM signal handling

asix uses the SIGTERM signal to rerun the simulation. Since SDL2
registers a signal handler, killing the old simulation does not have any
effect. The usual way to deal with that is to poll SDL events, but since
SDL is only used for audio here, a single line change does the job.

debian/patches/remove-sdl-signal-handler.patch

@@ -0,0 +1,12 @@
+--- a/src/tone/tone.cpp
++++ b/src/tone/tone.cpp
+@@ -248,7 +248,8 @@
+ 
+ void initTone() {
+ 
+-	if(SDL_Init( SDL_INIT_AUDIO ) < 0) {
++	SDL_SetHint(SDL_HINT_NO_SIGNAL_HANDLERS, "1");
++    if(SDL_Init( SDL_INIT_AUDIO ) < 0) {
+ 		printf("Erreur d'initialisation de la SDL : %s",SDL_GetError());//on affiche l'erreur
+ 		exit( EXIT_FAILURE);
+ 	}