fixes#361
Also, experminental introduction of vt_sounddata to enable tty to pass
a sound file index to the terminal side of things where perhaps someone
can add code to something like hterm to take the information relayed by
NetHack to trigger user_sounds locally even if playing on a server.
Compile time option TTY_SOUND_ESCCODES required to build that support in.
It should be independent of TTY_TILE_ESCCODES.
