Add support for overriding the output origin. For me, this was needed when I wanted to render directly into VA-API's encoder buffers, which are always top-left origin (and FBOs are always bottom-left origin).
Use GLSL 1.30-style attributes for the main shader. This is in preparation for removing fixed-function use altogether, for OpenGL 3.2+ core context support.
Kill the vertex shader system; it is too complicated to get it right until we have a full DAG understanding.