The code had previously set the cursor back to the standard arrow and unhid
it when it left all app windows.  Now it restores the cursor image that the
app set and re-hides it if necessary when it moves back over any app window.

Don't queue mouse-moved events.  Reset the cursor.

Some events get queued for all GUI-connected threads but are only processed
by the first to dequeue them.  Other threads which tend their event queue
discard such already-processed events.  However, some threads may be
connected to the GUI but never tend their event queue.  To prevent such
threads from accumulating zombie events, the zombies are cleared each time a
new event is queued.