GL_NV_register_combiners2
http://www.opengl.org/registry/specs/NV/register_combiners2.txt
	GL_PER_STAGE_CONSTANTS_NV 0x8535
	void glCombinerStageParameterfvNV (GLenum stage, GLenum pname, const GLfloat* params)
	void glGetCombinerStageParameterfvNV (GLenum stage, GLenum pname, GLfloat* params)
