[CM] snd and AC3

[Bill Schottstaedt]

I got a52dec and it seems to be fine, but I can't automate AC3 support in Snd
because, as far as I can tell, there's no way (besides the "ac3" extension) to
recognize an AC3 file.  You could call a52dec from Snd via 

(define (play-ac3 name)
  (system (format #f "a52dec ~A" name))

and something similar (see examp.scm OGG code) to translate such a file
so that Snd can edit it.