Ident construction example is incorrect in the presence of raw identifiers

The documentation for `Ident` has an example of how to make an ident with a name derived from another: https://docs.rs/proc-macro2/1.0.32/proc_macro2/struct.Ident.html#examples by just interpolating with `format!()`. However, it appears that if the original ident was raw, the output is invalid and unparseable: https://github.com/sfackler/rust-postgres/issues/839.

Is there any way of handling this properly other than something like `format!("__{}", ident.to_string().strip_prefix("r#"))`?