Rustdoc: re-exported ffi function metadata is not preserved.

[angdev]

std::mem::transmute is re-exported function of core::intrinsics::transmute.
Hyperlink of core::intrinsics::transmute is ~/ffi.transmute.html, not ~/fn.transmute.html, but source link of http://doc.rust-lang.org/std/mem/fn.transmute.html is http://doc.rust-lang.org/core/intrinsics/fn.transmute.html instead of http://doc.rust-lang.org/core/intrinsics/ffi.transmute.html

[UberLambda]

Having this code:

extern crate mycrate;
pub use alias = mycrate;

Rustdoc is unable to generate proper documentation for alias.
The [src] link on the alias page (doc_root/alias/index.html) is broken; it points to doc_root//alias/index.html, a malformed url, and doc_root/alias/ doesn't exist on my filesystem.

[steveklabnik]

Triage: link is still pointing to the same place.

[alexcrichton]

Fixed in #20081