* Killing debugger buffer no longer deletes the buffer's screen; that

* Killing debugger buffer no longer deletes the buffer's screen; that
  happens only when M-x browser-quit is invoked, and the screen was
  created for the debugger.

* Selection of a screen for a debugger buffer is now simpler.  If
  desired, a new screen is created (previously this was not an option
  if there was already more than one screen).  Otherwise, the current
  screen is used.  No other existing screen will ever be used.

* The X-windows-specific screen geometry stuff has been
  conditionalized so that it will not be used unless running under X.