Simulator terminates with zero exit code on error

[penberg]

We should make the simulator terminate with non-zero exit code so that external scripts, for example, can detect when it finds a problem.

[alpaylan]

I'll implement this on top of the minimization PR #623

edit: I just saw @LtdJorge opened a PR to fix it, but I would suggest we still do it on top of #623 because otherwise I'll just have to patch it anyway because it's a merge conflict.

[LtdJorge]

Don't worry, we can hold off my PR and I'll rebase it on top of yours. Or we can close it and you do your own version, whatever you prefer.

[alpaylan]

Both works for me, I can merge yours on top of mine too, shouldn't be too much of a hassle.

[LtdJorge]

Ok, I'll be tracking your PR