Feat(sync): when unpacking a sync file, if local data matches the sync data, don't update local file
Feat(sync): when unpacking a sync file, if local data matches the sync data, don't update local file

- Avoids redundant rewrites of local data; will occur if the syncdir is partially/totally removed and later
two machines with local files resync in series

jmquigs/greycrypt,jmquigs/greycrypt