The major patchset contributed by Michael Nauta has been committed. There are still some issues, and more might follow.
As the commit messag says:
4198: Person view does not remove a row correctly when two people are merged.

This is a major patch by Michael Nauta. It means all writes happen immediately to bsddb, and the bsddb
rollback is used on a crash. Transaction is no longer used to store changes and do them on commit.
Undo database is set on end.
At the same time with statement is used throughout for transactions
At the same time, the original bug in merge code should be fixed
Still some issues, that will be ironed out

I already found one bug, see http://www.gramps-project.org/bugs/view.php?id=4198

The things to watch out for however are lockups due to this change, and signal messages. So, we are again all guinea pigs for a while. I'll do further directed tests myself next days (eg making database crash).