core: derive Clone for result::IntoIter
core: derive Clone for result::IntoIter

It appears to be a simple oversight that `result::IntoIter<T>` doesn't
implement `Clone` (where `T: Clone`).  We do already have `Clone` for
`result::Iter`, as well as the similar `option::IntoIter` and `Iter`.

aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust