Added support for OpenGL ES and UIKit Video Driver: - included SDL_renderer_gles.h - added UIKit Video driver bootstrap declaration - added property "retained_backing" to gl_config structure. Having retained backing means your video buffers can't be overwritten by other applications between drawing frames. By default, this is enabled. I wanted to give the option to disable this on iPhone because it increases performance greatly. - modified SDL_GetAttribute and SDL_SetAttribute function for OpenGL ES support. OpenGL ES does not have support for accumulation buffers, and is always double buffered, among other things.