GL_S3_s3tc
http://oss.sgi.com/projects/ogl-sample/registry/S3/s3tc.txt
	GL_RGB_S3TC 0x83A0
	GL_RGB4_S3TC 0x83A1
	GL_RGBA_S3TC 0x83A2
	GL_RGBA4_S3TC 0x83A3
	GL_RGBA_DXT5_S3TC 0x83A4
	GL_RGBA4_DXT5_S3TC 0x83A5