rustdoc does not show where clauses in type aliases

Rustdoc does not show where clauses in type aliases

Code is:

``` rust
pub type MapFn<I, B> where I: Iterator = iter::Map<I, fn(I::Item) -> B>;
```

Renders in rustdoc as:

```
type MapFn<I, B> = Map<I, fn(I) -> B>;
```

The abbreviation of `Map` is great (it's a link), the loss of the associated types is probably bug #24417, but the where clause is missing too.
