 Lifetime bounds missing from re-exported items in documentation

Given:

``` rust
// foo.rs
pub struct Items<'a, T: 'a>;
```

``` rust
// bar.rs
extern crate foo;
pub use foo::Items;
```

Documentation for `bar.rs` shows `struct Items<'a, T>`, missing the lifetime bound. <del>This is still the case  on my branch in #17798</del>
