rustdoc: Inlined trait methods taking self by value don't show self argument

Compare http://static.rust-lang.org/doc/master/core/ops/trait.FnOnce.html:

> ``` rust
> pub trait FnOnce<Args, Result> {
>     fn call_once(self, args: Args) -> Result;
> }
> ```

 and http://static.rust-lang.org/doc/master/std/ops/trait.FnOnce.html:

> ``` rust
> pub trait FnOnce<Args, Result> {
>     fn call_once<Args, Result>(args: Args) -> Result;
> }
> ```
