The purported command output was already inaccurate, as the refs
aren't where it shows.  In any event, the labels a reader of this
file really needs are the indices used in commit_sorting_*, to make
it possible to understand them by referring directly from those
arrays to the diagram rather than from the index arrays, to commit_ids,
to the diagram.  Add those.

Signed-off-by: Greg Price <price@mit.edu>