Store combined output (stdout+stderr)

[njam]

Closes #1
Based on #3

[njam]

What doesn't work is if the command outputs to stdout and stderr immediately after each other (without any delay). I believe the reason is that ruby loop is too slow, so that when I check the next available IO objects both are already available.

I think this happens very rarely in real life though. I added a skipped spec for that.

What do you think?

[coveralls]

Changes Unknown when pulling ba88176 on njam:output-combined into * on collectiveidea:master*.

[njam]

Moving this to a new repo: https://github.com/cargomedia/komenda