Can't infer generic integer constants as floating-point

```
fn main() {
    let x: f64 = 2.0;
    println!("{}", x / 2);
}
```

Returns:

```
expected `f64` but found `<generic integer #0>` (expected f64 but found integral variable)
```

Easy fix is to change the `2` to a `2.0`, although that seems kind of excessive in this case. It makes more sense to make integer constants generic numbers, like Haskell does, if they're going to be generic.
