Allow at_exit handlers to run when aborting runs

[jdelStrother]

At the moment, if you hit Ctrl-C twice to abort a run, rspec uses exit! to exit, so at_exit handlers aren't run. This means, for example, that Capybara doesn't send a quit message to its browser, so I often end up with dead Google Chrome processes lying around.

I'm not sure what the rational was for choosing exit! vs exit (/cc @dchelimsky ?), so I'm not 100% convinced this PR is correct/desired behaviour. Would welcome any thoughts on it.

[myronmarston]

This is intentional. To exit with proper cleanup/shutdown, hit ctrl-c once. RSpec attempts to gracefully shutdown after the first ctrl-c. You can hit ctrl-c a 2nd time to force it to immediately shutdown, without any cleanup. We use exit! in this case because it forces an immediate exit, where as exit triggers at_exit handlers, which, as they run user code, could hang and prevent the interpreter from immediately exiting. So I don't think it would be appropriate to use exit on the 2nd ctrl-c, as it would go against the goal of immediately exiting.

Is there some reason why a single ctrl-c isn't working properly for you? Maybe there's something we could improve there so it exits more quickly while retaining the cleanup it performs.

[jdelStrother]

I use double-ctrl-c when I’ve already seen what I want from a run and don’t care about waiting for the current spec to finish. I kinda think it’s a weird thing for rspec to provide - eg rake doesn’t override interrupt signals on the off-chance that someone’s at_exit handler might be misbehaving. Why do you think rspec should?

[xaviershay]

I believe historically we've had sufficient issues with rspec not exiting at all in response to ctrl+c that we made it follow current behaviour.

[JonRowe]

I agree with @myronmarston and @xaviershay here, the current behaviour is desirable, you can achieve your goals by only hitting ctrl-c once.