1) Ciolib CIO_KEY_QUIT and CIO_KEY_MOUSE conflicted with ALT_7 and ALT_6
   respectively, change these to use \xE0 prefixes.
2) Add a new dorkit key "CONNECTION_CLOSED" which is returned by getkey()
   after the connection is closed.
3) Have the various connection back-ends send a CONNECTION_CLOSED key to
   the keyboard buffer when the connection is closed.
4) Have the local console send a CONNECTION_CLOSED key when the window
   is closed.
5) Disable auto_terminate in dorkit.
6) Introduce dk.connection.disconnect_timeout variable (defaults to 30
   seconds).  After a CONNECTION_CLOSED key is received, dorkit will
   immediately set js.terminated, then after disconnect_timeout seconds,
   will enable js.auto_terminate.
7) After a CONNECTION_CLOSED key, waitkey() always returns true, getkey()
   always returns a CONNECTION_CLOSED key, and getbyte() always returns
   undefined.
8) To prevent a poorly written door from hogging 100% CPU for the whole
   30 seconds, put an mswait(1) in the connection check when the
   inactivity timer is running.