Stack overflow with use of `Self` in inherent impl on trait

```
pub trait ToNbt<T> {
    fn new(val: T) -> Self;
}

impl ToNbt<Self> {}

fn main() {}
```

```
thread 'rustc' has overflowed its stack
Illegal instruction (core dumped)
playpen: application terminated with error code 132
Program ended.
```

Playpen: http://is.gd/TStXZ9
Thanks @huon helps.
