Jittering, Aliasing

One of the funnier issues with WinterBoard on 2.1 is that icons, while jittering (during movement), were getting weird border effects that looked pretty bad. Not only have I fixed these issues but I've made the effect work better than Apple's original code (you will have noticed that, for example, the iPod icon always had a little of this effect on the sides). Please note that this improvement is only available on 2.1 (on 2.0.x it will work like Apple's stock rendering algorithm, which is still very good).