Data format changes will need to be backported to 4.2:
- Make bit flags in cell.h for the extra descriptor byte match those (newly added) in 4.4.
- Ignore any cells marked as "prepared", but issue a warning message.
- Add code as appropriate (cell reading code in btree and salvage) to skip over the new durable stop timestamp.
Because of the importance of finalizing the 4.2 changes early on, it might be good to test this via an ad hoc method: modify (hack!) a 4.4 system to write out certain updates as prepares, with and without the durable stop timestamp set. Use this to generate files that can be tested with 4.2. If we wait to test this when the prepare support for DH is nearing completion, we may need to make 4.2 changes at the last minute.