Shape::contains_point fails with big numbers

Why does this code fail? Making the 1e19 small enough (1e18) eventually makes it work, but that seems quite _ugh_. Is this expected behavior?

```rust
let poly = ConvexPolygon::try_from_points(&vec![
Point::new(1600.0f64, 100.0),
Point::new(10100.0, 1958.0),
Point::new(1e20, 1958.0),
Point::new(1e20, 100.0),
]).expect("Convex hull computation failed.");

assert!(poly.contains_point(
&Isometry::identity(),
&Point::new(1e19, 300.0)
));
```