Do not panic in OsIpcOneShotServer::new

[xmakro]

Currently OsIpcOneShotServer::new can panic in (see code):

let temp_dir = tempfile::Builder::new().tempdir().unwrap();

It would be good to raise the error instead. This would require modifying UnixError to have a variant Io(io::Error). This makes the UnixError struct larger and non copyable, but UnixError is converted to io::Error later on, this might be okay.

If you agree with this change, I'd send a PR.

[jdm]

Agreed! I would merge a PR.