[devtools] write db config through a temporary file
Avoids other test processes reading partially written config and
exploding in pickle.loads. There are still concurrency issues,
presumably with the database itself. Something for another friday.
[server] Add missing indices for undo support (closes #3259691)
The tables used by the 'undo' feature were missing some indices, which
among other things triggered repeated sequential scans when deleting old
transactions.