Dreamfall Chapters: Partial fix for light shafts

I've been staring at this too long and fudging too much of the maths.

Can't get it right...

Time to move on.

U should toggle between the partial fix, mono and disabled.
Dreamfall Chapters: Apply same partial fix to other light shaft final interpolation shaders

I'm pretty sure I also need the fix in the coords and raymarch shaders,
but only once it is correct. Putting in this fudged fix just makes the
light shafts look weird as each section of the ray is interpolated in
the wrong direction.