Associated types in traits used as bounds are treated as type arguments

When using a trait with an associated type as a bound on a type argument, its associated types are treated as arguments rather than as determined by the impl:

``` rust
trait Foo {
    type T;
}

trait Bar<F: Foo> {
    fn bar(foo: &F);
}
```

```
error: wrong number of type arguments: expected 1, found 0
```

http://is.gd/KPP4ka
