GLSL Debugging Continues!
So, I made SOME progress on debugging GLSL using Apple's Shader Builder, which you can download from http://developer.apple.com/downloads, with a free Apple Developer's account.
Though, this morning I'm reevaluating this approach. While, I often find doing such exercises are massively educational, they are often a exercise in futility.
I'm thinking, now, that I might best find my time productive if I target libGDX's Default Shader. It's set up nice, in a largely modular way, lots of #includes, etc. When I finish, I can commit the result to source, so others might benefit from my labor.