Remove unnecessary redisplays in NS port.

Remove unnecessary redisplays in NS port.

* nsmenu.m (update_frame_tool_bar): Set wait_for_tool_bar to NO
when setNeedsDisplay is called so we don't trigger redisplay for every
tool bar update.

* nsterm.m (any_help_event_p): New variable.
(mouseMoved:): Set any_help_event_p to YES if help event is
generated.  Remove else with empty help event that triggered redisplay
for every mouse move.
(windowDidResignKey:): If any_help_event_p, generate empty help
event.