Private type error has poor span and inaccurate phrasing for private traits used as bounds

[huonw]

pub fn foo<T: Bar>() {}

trait Bar {}

priv-trait.rs:1:12: 1:13 error: private type in exported type parameter bound
priv-trait.rs:1 pub fn foo<T: Bar>() {}
                           ^
error: aborting due to previous error

The span should point to Bar (especially important for param lists with several traits), and it could probably say trait instead of type.