I accidentally `-torcontrol=1` today (instead of `-listenonion=1`) and was confused that it was accepted, as the argument needs to be `host:port`. Expected outcome would be an error message and exiting. #### Useful skills: - C++ - Understanding of bitcoin core's initialization sequence #### Want to work on this issue? For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.