GL_EXT_texture_shared_exponent
http://developer.download.nvidia.com/opengl/specs/GL_EXT_texture_shared_exponent.txt
	GL_RGB9_E5_EXT 0x8C3D
	GL_UNSIGNED_INT_5_9_9_9_REV_EXT 0x8C3E
	GL_TEXTURE_SHARED_SIZE_EXT 0x8C3F