Consider revisiting some details of Display for io::Error

[nox]

The implementation of Display for io::Error currently completely omits the kind of the error for errors created with io::Error::new.

Do you think it would be possible to change that and include it for all others whose kind is not io::ErrorKind::Other? I realise that this is probably a breaking change, but I wonder if there is that much code out there using io::Error::new with a kind different to io::ErrorKind::Other.

[JDuchniewicz]

Do we know the rationale behind not printing them in the first place? I presume that unwillingness to print out every member of the io::ErrorKind enum was the main reason.

[nox]

Digging way too far in the past I've found out that it actually used to be that way.

[nox]

It was then changed to always ignore the error kind for custom errors in this commit.

[nox]

AFAICT, the PR never explains why that change was made. Do you remember, @alexcrichton?

[alexcrichton]

Sorry, I do not.