git-rev-list: allow missing objects when the parent is marked UNINTERESTING
git-rev-list: allow missing objects when the parent is marked UNINTERESTING

We still want the "top-most" uninteresting object to exist, so that we
know that we have reached it.

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git