Saner speaker process design

 - device_state now records what state we think the output device is
   in.  For network/command the open/close state is somewhat
   fictitious.
 - mainloop now decides whether it wants to play audio sensibly
   (playable()) and only calls beforepoll() and ready() [formerly
   afterpoll()] if so
 - error retry done at the same time but without calling ready()
 - play() is now defined as always safe to call, and makes best
   efforts to be able to play something.
 - forceplay is gone