rustdoc creates bad links on pub use of enum variants

[chris-morgan]

The std prelude contains pub use option::{Option, Some, None}.

rustdoc turns the prelude into http://static.rust-lang.org/doc/master/std/prelude/index.html. In the process, it makes a mess of pub use'd enum variants such as Some and None, turning them into bad links like http://static.rust-lang.org/doc/master/std/option/Option/variant.Some.html. You see, rustdoc doesn't produce pages for enum variants—it only produces pages for the containing enum. The Enum/variant.Variant.html needs to be changed to enum.Enum.html. No need for a hash.