Stop plotting, but keep copying

[cross]

Sometimes, when I have a system that isn't plotting well, I want to change parameters. But it takes many hours to plot, so I'll typically let one finish. Often, though, I'm left in the situation where I'd asked for 2 or more plots, then decide I want to stop it after it finishes the first. But, if on slow disks, it will start plotting the next plot which I want to stop, while still copying the first.

Please add some sort of signal handling so I could perhaps send the plotter an interrupt, but have it know that means "stop plotting, but finish any outstanding copies before exiting."