`lines-changed-only` should assert `files-changed-only` implicitly

User intuition probably implies that the `lines-changed-only` option should implicitly mean `files-changed-only` is true, but this is not the case under the hood.

I think this is partially implemented in #81 (as part of the solution to #74), but it would be better to make the source explicitly change the value of `files-changed-only` if `lines-changed-only` is not disabled.