[Blindness] Auto-reveal & straight Shapes

[Karl DD]

With Blindness turned on and using the Shapes module in straight shape mode, the canvas is not kept hidden until the shape finishes.
Mouse up is the event which triggers the auto-redraw in the Blindness module, however with straight shapes this is not what you would expect. Need to implement some global behaviour for this, rather than dirty each module with module-dependant code.