ensure no memory leaks, bad memory accesses in SDL port

[dmalan]

[cmlsharp]

This is a bit tough to ensure since valgrind will show leaks for any SDL program (source). At this point, I can at least say that all the errors reported after a full game of breakout seem to be coming from SDL itself. That said, much more testing is required.

[dmalan]

Okay, do report back!