Oops!

As for other options?  I don't *think* so; at least not at the moment.  (Amusingly, I had duplicated these constants before I realized that they already existed.  So actually you were really on top of this.)

I think that we'll want to add some more that drive the merge engine (prefer ours / prefer theirs for line-level conflicts) which are (in this PR anyway) defined as flags to git_merge.  They probably belong in checkout opts, even though git-checkout wouldn't expose these options.  But I'm not entirely certain yet.