Adding self parameter to trait causes code to segfault

The following snippet segfaults when run.  Removing the "self" parameters to thingie makes it not segfault, but makes rustc tell me that form is deprecated.

```
pub trait TestTrait {
  fn thingie(self) -> ~[u8];
}

impl ~[u8]: TestTrait {
  fn thingie(self) -> ~[u8] {
    ~[0u8]
  }
}

fn main() {
  let n = ~[];
  n.thingie();
}
```
