rustdoc: External implementors for inlined traits are not shown

[mitaa]

When re-exporting a external trait, the implementors section of that (inlined) trait does not show external implementors of it (unless they too have been inlined).
Re-exported external types on the other hand do show external trait implementations.

// foo.rs
extern crate bar;

pub use bar::Bar;

// bar.rs
pub trait Bar {}
pub struct Baz;

// this impl does not show up in `foo::Bar`s implementors section
impl Bar for Baz {}