[SDL] Full screen mode disabling screensaver?

[Ryan C. Gordon]

> What about a "SDL_AllowScreensaver(bool allowit)" ?

Because there's an unspoken policy: no more API changes in 1.2.

Also, an environment variable says "this isn't a formal SDL thing, it's 
a hack" and you don't have to promise it works on every platform.

For SDL 1.3, though...maybe. I feel like I take way too many liberties 
in saying what we will and won't do when it's really not my call.

--ryan.