Problem: Some tests fail on Cirrus CI and/or with FreeBSD.
Solution: Make 'backupskip' empty. Do not run tests as root. Check for
directory when using viminfo. (Ozaki Kiichi, closes#6596)
Problem: Using a full path is supported for 'directory' but not for
'backupdir'. (Mikolaj Machowski)
Solution: Support 'backupdir' as well. (Christian Brabandt, closes#179)