* Initialize audio buffer to correct silence value. This prevents
popping when the recording didn't set the entire buffer
* Select different devices when pulseaudio is the active
  driver. Evidently launching from Emacs will cause a different audio
  driver to be active (alsa from Emacs, pulseaudio from the command
  line)
* Abort audio initialization if either device fails
* Update Cakelisp for --execute option