Downgrade term crate back down to 0.2 (from 0.4).

Downgrade term crate back down to 0.2 (from 0.4).

This is undoing part of commit dd34296

Fix #2338

(Unfortunately I do not have a suggestion for how to make a unit test
for this problem; doing so would require putting in a bit more effort
than I have time for at the moment.)