GL_EXT_422_pixels
http://oss.sgi.com/projects/ogl-sample/registry/EXT/422_pixels.txt
	GL_422_EXT 0x80CC
	GL_422_REV_EXT 0x80CD
	GL_422_AVERAGE_EXT 0x80CE
	GL_422_REV_AVERAGE_EXT 0x80CF