RSX : add rescale support for native 960x1080 & 1024x768

Beer Pong should be now rescaled correctly in 480p/720p/1080p with its strange native 960x1080 res

![untitled](https://cloud.githubusercontent.com/assets/3000282/3494433/d691bfae-05c5-11e4-8f68-0633a54c1ada.jpg)

(I will simplify this urgy code shortly)