p2 revolute pivots were wrong signed

I was unsure if my my mind was twisted or if this is a bug. Seems not to be my mind in this case. I drew some shapes on the bodyDebug and here you can see the previous and fixed version. The red dot shows the pivot. The error is obvious in the first image.

![bug](https://f.cloud.github.com/assets/1701755/2481259/38d81ec8-b0d6-11e3-8ace-c09b516d0cba.png)
![fixed](https://f.cloud.github.com/assets/1701755/2481258/38d709fc-b0d6-11e3-8d66-6e1af448c22f.png)