Impl on type imported unqualified from different module

``` rust
pub struct Foo;

mod bar {
    use Foo;

    impl Foo {
        fn baz(&self) {}
    }
}
fn main() {}
```

```
qualified.rs:6:10: 6:13 error: found module name used as a type: impl bar::Foo::Foo (id=10)
qualified.rs:6     impl Foo {
                        ^~~
```
