Revisit complex backup scenarios

[rrrooommmaaa]

After #4059, #4060 and #956 are fixed.
Test that redirection from backup to change_passphrase and back to backup (with Settigns.redirectSubPage) doesn't break messaging setup (e.g. password_dialog message to settings/index.htm) if required.

Test change_passphrase for non-primary key due to weakness found in encryptForBackup()