0006529: Cancelling database upgrade can corrupt the database. Check whether the bsddb version has changed (or was originally unknown). If it is an upgrade, ask the user whether he has made a backup, and is ready to upgrade. If so, made a zip backup and open the database with the new bsddb version. Make messages on the dialogues more explicit with the version numbers mentioned.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21852 4ae1f11a-8b86-4847-b8af-ab372f36d1fd