Typing for second variable in for

```rust
for (n, i) in 0..10 {
    ...
}
```

In a `for` loop, the second variable (if provided), in this case `i`, is always `int` at the beginning of each iteration, so this can probably be hard-coded in.

Technically speaking we can infer the type of `n` from the range operator as well, but that is not 100% fool-proof.
