code: func NewCommitIter(s storer.EncodedObjectStorer, iter storer.EncodedObjectIter) CommitIter {
  	return &storerCommitIter{iter, s}
  }
docs: // NewCommitIter takes a storer.EncodedObjectStorer and a
  // storer.EncodedObjectIter and returns a CommitIter that iterates over all
  // commits contained in the storer.EncodedObjectIter.
  //
  // Any non-commit object returned by the storer.EncodedObjectIter is skipped.