Segmentation fault on safe test panic

This is as minimal an example as I've been able to reduce this to so far:

``` rust
fn f(_: Vec<u32>, _: &Vec<u32>) {
    panic!();
}

fn identity(r: &Vec<u32>) -> &Vec<u32> { r }

#[test]
fn t() {
    f(vec![0], identity(&Vec::new()));
}
```

```
$ rustc --version
rustc 1.0.0 (built 2015-05-22)
$ rustc --test foo.rs
$ ./foo 

running 1 test
Segmentation fault
$ 
```
