GL_EXT_texture_compression_s3tc
http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt
	GL_COMPRESSED_RGB_S3TC_DXT1_EXT 0x83F0
	GL_COMPRESSED_RGBA_S3TC_DXT1_EXT 0x83F1
	GL_COMPRESSED_RGBA_S3TC_DXT3_EXT 0x83F2
	GL_COMPRESSED_RGBA_S3TC_DXT5_EXT 0x83F3