Apparently in zsh (when in sh compatibility mode), IFS=/ will split
"/a/b/c/" into 5 parts ("", "a", "b", "c", ""). Other shells all seem
to agree that it's 4 parts ("", "a", "b", "c"). zsh seems maybe more
correct to me, but the majority rules, so we'll warn on it.

Meanwhile, we'll also fix the one place in minimal/do that failed due
to this oddity, since it's relatively easy to avoid.

Reported-by: shamrin@gmail.com