Remove unnecessary forward decls.
(struct sound_device): The 'file' member is now a Lisp_Object, not
a char *, so that we needn't invoke alloca on a huge size.
(Fplay_sound_internal): Adjust to this.
(string_default): New function.
(vox_open, vox_init, alsa_open, alsa_configure, alsa_init):
Use it to adjust to the struct sound_device change.
(parse_sound, wav_init, au_init, alsa_init): Use bool for booleans.
(be2hs) [0]: Remove.