Added SDL_GL_RETAINED_BACKING to SDL_GLattr enum. Retained backing means the memory for color buffers, depth buffers, etc cannot be overwritten by other applications between frames. The default for this setting is 'on'. I wanted to add this because turning retained backing off on iPhone dramatically increases performance.

#ifndef _SDLname_h_
#define _SDLname_h_

#if defined(__STDC__) || defined(__cplusplus)
#define NeedFunctionPrototypes 1
#endif

#define SDL_NAME(X)	SDL_##X

#endif /* _SDLname_h_ */