Eventually, it'll make sense to replace all the references to
"rio" with "nile". At that point, I'll have to stop referencing the
rio source for otherwise-unchanged files, and the diffs will
get a lot more tedius to read. Putting it off for now.

For future consideration:
•	Cinap has a patch for rio.c to set a background inage,
	allow window cycling via kbd (& mouse?), change to pie
	menus. See /n/sources/contrib/cinap_lenrek/rio.c
		(Don't yet understand ZP changes)

•	I'd like wctl to be able to toggle the scroll state, not just
	set it on or off. Alternately (additionally?), it'd be useful
	to be able to query the current state. Then I could add
	Scroll to my modified winwatch's menu.