cairoblur: Fix the blur again once more
cairoblur: Fix the blur again once more

The differences between the mutter and GTK+ code are subtle, but it
turns out that _gtk_cairo_blur_compute_pixels actually returns the
shadow *spread*. Since we use a triple box blur, the constant was
multiplied by 1.5 to approximate three chained box blurs. Split this
out and use the correct value for the lobe width.

jigpu/gtk,jadahl/gtk,jadahl/gtk,ahodesuka/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,chergert/gtk,alexlarsson/gtk,Lyude/gtk-,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,Adamovskiy/gtk,alexlarsson/gtk,ahodesuka/gtk,jigpu/gtk,jadahl/gtk,ahodesuka/gtk,jigpu/gtk,alexlarsson/gtk,Lyude/gtk-,grubersjoe/adwaita,chergert/gtk,grubersjoe/adwaita,jadahl/gtk,Lyude/gtk-,alexlarsson/gtk,grubersjoe/adwaita,Adamovskiy/gtk,Adamovskiy/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,Lyude/gtk-,grubersjoe/adwaita,davidgumberg/gtk,Lyude/gtk-,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,ahodesuka/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,jadahl/gtk,jadahl/gtk,jadahl/gtk,chergert/gtk,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,ahodesuka/gtk,Adamovskiy/gtk,alexlarsson/gtk,Lyude/gtk-,ahodesuka/gtk,Lyude/gtk-,davidgumberg/gtk,ahodesuka/gtk,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,Adamovskiy/gtk