GLX_EXT_visual_rating
http://www.opengl.org/registry/specs/gl/EXT/visual_rating.txt
GLX_EXT_visual_rating
	GLX_VISUAL_CAVEAT_EXT 0x20
	GLX_SLOW_VISUAL_EXT 0x8001
	GLX_NON_CONFORMANT_VISUAL_EXT 0x800D