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 think there's a lot of bad precedent in deal.II :-( By the way, you don't even need it, you could just use
  Point<dim>::unit_vector(i);

It's ok if you wanted to change it in CylinderBoundary, but I figure that that class will eventually be obsoleted/deprecated anyway, so maybe it's not worth putting any new work into it.