GL_EXT_pvrtc_sRGB
http://www.opengl.org/registry/specs/EXT/pvrtc_sRGB.txt
GL_EXT_pvrtc_sRGB

	GL_COMPRESSED_SRGB_PVRTC_2BPPV1_EXT 0x8A54
	GL_COMPRESSED_SRGB_PVRTC_4BPPV1_EXT 0x8A55
	GL_COMPRESSED_SRGB_ALPHA_PVRTC_2BPPV1_EXT 0x8A56
	GL_COMPRESSED_SRGB_ALPHA_PVRTC_4BPPV1_EXT 0x8A57
