Rustdoc search does not find inherent methods on primitive types

Searching on rustdoc for a inherent method on a primitive type (e.g. [width](http://doc.rust-lang.org/nightly/std/?search=width)) does not find it, even if it [exists](http://doc.rust-lang.org/nightly/std/primitive.char.html#method.width).

cc https://github.com/rust-lang/rust/pull/23104.
