CylindricalManifold implementation

I adapted this from the old Manifold branch. 

Here is how it looks:

![screen shot 2014-08-06 at 14 53 07](https://cloud.githubusercontent.com/assets/2919756/3827061/8c01c130-1d69-11e4-9345-d61d218bd522.png)

I marked it protected, because derived classes (like, in this case, cylinder manifold) use a tolerance for distances, and I make them all use the same tolerance instead of having all of them  define their own tolerance...