TarError::Io returns exit code 2, GNU tar returns exit code 141

[kevinburke]

In extract.rs, code like this

out.flush().map_err(TarError::Io)?;

UError::code reports as 2, with the io error printed to stderr - is non-conventional. GNU tar on tar tf foo.tar | head -1 exits via SIGPIPE (status 141) silently