* (update-screen!): Clear the NEEDS-UPDATE? of the screen if the

* (update-screen!): Clear the NEEDS-UPDATE? of the screen if the
  update finishes properly.

* (screen-force-update): Fix typo that caused the new and current
  matrix lines of highlighted text to become EQ?.

* (with-screen-in-update): Eliminate UNWIND-PROTECT since interrupts
  are locked while it executes and any errors in the redisplay
  indicate a serious problem that makes the UNWIND-PROTECT
  uninteresting.

* (with-screen-in-update): Avoid calling SCREEN-UPDATE if the screen's
  NEEDS-UPDATE? flag is not set.

* (with-screen-in-update, screen-update): Don't update the cursor
  position unless the screen update finishes and the cursor has moved.

* (screen-update): Avoid use of FIX:REMAINDER, which is not open-coded
  on the MIPS.

* (screen-update): Change meaning of PREEMPTION-MODULUS so that it
  counts the number of updated lines rather than the number of lines.
  This avoids unnecessary work when only a few lines need changing,
  such as when only the modeline or typein window is being updated.
  Because of this change, eliminate DEBUG-PREEMPTION-Y from the SCREEN
  structure since it is no longer easy to simulate preemption like
  this (and this debugging tool was never needed).

* (update-line-highlight): When comparing old and new lines, don't
  consider short matches since it is usually cheaper to ignore them.
  This has already been done for the no-highlight case and should have
  been done for this case at that time.