[Etoys] Screen damage issues when dropping tiles in ScriptEditor

[Yoshiki Ohshima]

> When I turn on preference showDebugDamage there are some
> issues when dropping tiles in the ScriptEditor. A rectangle in the
> top left corner flashes, and a large part of the screen is redrawn when
> the tile is dropped, from top left of screen to bottom right of 
> ScriptEditor.
> I guess this will slow the tile scripting responsiveness.
> Also the Viewer flap tabs are redrawn quite often, not flap tabs for 
> SketchMorphs, but for other morphs.
> Karl

  Thanks Karl for reporting!  We did use showDebugDamage when damage
rectangle merging was too eagar^^; But after that we didn't look at
other places with the option turn on yet.

-- Yoshiki