multiline input > terminal height is broken

[strtok]

There's a few ways to see symptoms of this:

1. Start a multiline prompt and add enough lines so that the prompt scrolls above the terminal window. Scroll up with the terminal and you will see that multiple prompts have been rendered, likely as an effect of how the refresh() code deals with refreshing a terminal.
2. Input enough lines so that the terminal prompt scrolls above the terminal window, and then arrow up. It is not possible to arrow up to the text that scrolled away.

This is tracked in the rustyline project by kkawakam/rustyline#611