Comment 1 for bug 622454

Changing the Commit signal from:

  Commit(av row_data, au positions, au change_code, at seqnums)

to:

  Commit(av row_data, au positions, ay change_code, (tt) seqnum_before_after)

So 'change_code' becomes just one byte, and we don't transfer all the intermediate seqnums because they *must* be in sequential order (n, n+1, n+2, n+3,...) anyway so it's redundant info. These to changes cuts significantly don't on the message sizes.