Nitpicking: visibility errors on a tuple struct count fields from 1 when the language counts them from 0

``` rust
mod m {
    pub struct S(i32);
    pub const K: S = S(0);
}

fn main() {
    0 == m::K.0;
}
```

```
<anon>:7:10: 7:16 error: field #1 of struct `m::S` is private [E0451]
<anon>:7     0 == m::K.0;
                  ^~~~~~
<anon>:7:10: 7:16 help: see the detailed explanation for E0451
```
- https://play.rust-lang.org/?gist=d090346cd5446b09a7d4&version=nightly
