'assertion failed: rp.is_none()' during compile

Code to produce

```
pub mod bits {
    use std::vec;
    use std::uint;

    struct BitVector<'self> {
        v: &'self [u8]
    }

    pub fn new(n: u64) -> BitVector<'self> {
        let f = vec::with_capacity::<u8>(n);
        BitVector {
            v: f
        }
    }
}


fn main() {
    let f = bits::new(10);
}
```

Backtrace is here https://gist.github.com/5864573
