Improve error handling

[igorko]

Discovered while trying to load GameStateLoad screen on Polymorphable with Flare savegame in the list. Also added exit(1) where needed to really terminate app correctly.

[igorko]

oops. It doesn't build.

[stefanbeller]

In http://sdl.beuc.net/sdl.wiki/SDL_Quit they say we could also use atexit(SDL_Quit);
Not sure what's the best approach though.

Note: While using "atexit" may be be fine for small programs, more advanced users should shut down SDL in their own cleanup code. Moreover, using "atexit" in a library is a sure way to crash dynamically loaded code.

[igorko]

No idea why that exit(1) is blamed by g++, but we can leave without it ;)

[ghost]

There's a member variable named "exit" in MenuManager. You can probably use something like "std::exit(1)" to avoid the name collision.

[stefanbeller]

Another idea would be to put the exit (or abort function?) together with a previous SDL_Quit into a function, as the sequence

SDL_Quit()
exit(1);

happens to appear quite often now.

[clintbellanger]

Consider this a short-term fix. During Beta we will have better clean-up code that will attempt to free memory properly.