Do not error a stream when another stream only aborted

[ehmicky]

Execa pipes multiple streams internally. For example {stdin: webStream} pipes webStream to childProcess.stdin. Also, transforms pipe with each other and with childProcess.std*.

We pipe the source and the destination stream with source.pipe(destination). When either aborts or errors, we destroy the other stream, for cleanup and error handling purposes.

Node.js streams distinguish between aborting (stream.destroy()) and erroring (stream.destroy(error)). The propagation logic described above currently does not make that distinction. So when a stream is aborted, the other streams are errored instead of being aborted as well.