Traits with associated types break in struct bounds

``` rust
#![feature(associated_types)]

trait PoolManager {
    type C;
}

struct InnerPool<M: PoolManager> {
    manager: M,
}

fn main() {}
```

```
test.rs:7:21: 7:32 error: no suitable bound on `<generic #0>`
test.rs:7 struct InnerPool<M: PoolManager> {
                              ^~~~~~~~~~~
error: aborting due to previous error
```
