rustdoc generates bad fragments in links to trait methods

[eefriedman]

For example, https://doc.rust-lang.org/nightly/std/net/enum.SocketAddr.html links to "https://doc.rust-lang.org/nightly/std/fmt/trait.Display.html#method.fmt", but the correct link is "https://doc.rust-lang.org/nightly/std/fmt/trait.Display.html#tymethod.fmt".