ICE: rustc stack overflow error w/ recursive types

Given the following code:

``` rust
trait Stream<T, N: Stream<T>> {
}

pub fn main() {
    println!("zomg");
}
```

Running rustc gives the following output:

```
task 'rustc' has overflowed its stack
[1]    47380 illegal hardware instruction  rustc types.rs
```
