segfault on vector.filter

There's a segfault when running the following code (it compiles fine).

``` rust
fn main() {
  let v = ~[1,2,3,4];
  let b = v.filter(|&i| i > 1);
}
```

Changing `|&i| i > 1` to `|i| *i > 1` does not fix the problem. However, using the vec::filter function instead of the method does not segfault.

Possibly related: https://github.com/mozilla/rust/issues/4878
