More JavaDoc for function for upgrading database version:
- Tell developers to use the startup database integrity test to see whether their upgrade code works
- Fixes issue https://bugs.freenetproject.org/view.php?id=6186
Don't consider enum Objects as database leaks:
- Db4o creates them automatically, and they cannot be deleted. See added comment.
- This fixes https://bugs.freenetproject.org/view.php?id=5965