* renderer_opengl: Namespace OpenGL code
Namespaces all OpenGL code under the OpenGL namespace.
Prevents polluting the global namespace and allows clear distinction
between other renderers' code in the future.
* Also namespace TextureCubeConfig
This was very likely intended to be a logical OR based off the
conditioning and testing of inversion in one case.
Even if this was intentional, this is the kind of non-obvious thing one
should be clarifying with a comment.
