ICE when using rust-core-foundation's CFDictionary type

Here's a backtrace of the failure: https://gist.github.com/metajack/5548289

And here's a small failing program:

``` rust
extern mod core_foundation;

use core_foundation::base::{CFTypeRef};
use core_foundation::string::{CFStringRef};
use core_foundation::dictionary::{CFDictionary};

fn main() {
    let _dic = CFDictionary::new::<CFStringRef, CFTypeRef>([]);  
}
```
