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.
Showing with 20 additions and 5 deletions