Private items with a public reexport could suggest the public path in privacy error message

[huonw]

E.g. use std::io::buffered::BufferedReader; says struct BufferedReader is private but could say

struct BufferedReader is private, but available publicly as `std::io::BufferedReader`

(This probably requires some significant work, for not a huge benefit.)

[steveklabnik]

Triage: no change here, these kinds of messages still happen.

[steveklabnik]

Triage: no change