I think making the inserter here in Merger was a mistake. We should try to share the inserter with the caller who wants to create a commit object. That way on the DFS system we write a single pack with the new blobs/trees/commits at once, rather than 2 packs (one with blobs/trees from merger, the other with a single commit by itself).

This would also give the ODI a chance to consider putting that commit into the pack if it chose to do the other inserts as part of a pack.