Flip coordinates left/right-handed for OpenGL refraction

This is a separate writeup following up on an earlier "first impressions" posting.

On non-DirectX renderers, some shaders like refraction need to flip the Y coordinate to work properly.  Since non-DirectX means Mac, Android, iOS, and pretty much everything but Microsoft, I hope it gets supported.

When building a project for multiple platforms, will a shader be compiled multiple times?  If so, there should be an #ifdef pragma to control shader compiles for feature differences like this.