Added special strdup to liboptions, to prevent memory leaks for option strings

If you are doing memory leak debugging you don't want to see any leaks when
stopping the program.

src/libsound/sound_alsa.c

@@ -197,7 +197,7 @@ void *sound_open(const char *audiodev, double __attribute__((unused)) *tx_freque
 		return NULL;
 	}
 
-	sound->audiodev = strdup(audiodev);
+	sound->audiodev = strdup(audiodev); // is feed when closed
 	sound->channels = channels;
 	sound->samplerate = samplerate;
 	sound->spl_deviation = max_deviation / 32767.0;