Restore handling of relative values for `database.path` that was
broken by 0.32. Extend this handling to `database.mail_root`,
`database.backup_dir`, and `database.hook_dir`.
Restore handling of relative values for `database.path` that was
broken by 0.32. Extend this handling to `database.mail_root`,
`database.backup_dir`, and `database.hook_dir`.