[[CHORE]] Make some test assertions that want a single error explicit.
[[CHORE]] Make some test assertions that want a single error explicit.

In the new tests, (and testOverrides that they were templated from), the
assertions in the failure cases now check for exactly one error, rather
than just more than zero.

thomas658/jshint,jshint/jshint,thomas658/jshint,jshint/jshint