die when connection is lost

[jonahkagan]

Right now the repl just stays open when, say, your internet goes down. I think it might also reconnect when it comes back, which is nice I guess, but the problem is that when you type a command in a repl that isn't connected to a db, it hangs for a while until it the command fails before dying, and then you lose that command from history. It would be better to just die like the mongo shell does.