request: more refined termination behavior

[mcandre]

When the user is currently running a foreground process in the shell, such as an SSH session or long-running Rust compilation, then I want the terminal to warn when sent a signal to close the window or quit the terminal application, like Terminal.app does.

Currently, rio only applies the simple true/false confirm-before-quit logic, when deciding about prompting before ending the window/application.

I never want to see a confirmation to end the program unless I have an ongoing foreground process.