Release of 6.4.0

* Wed Oct 21 2020 Chris Tessmer <chris.tessmer@onyxpoint.com> - 6.4.0-0
- Added check for dangerously unspecific OS versions in `unpack_dvd`
  (e.g., '7' instead of '7.0.2003').  This is common when autodetecting the OS
  version from the ISO's .treeinfo on some OSes (particularly CentOS).
  - When detected, script will exit with an informative message + instructions.
  - In this case, users should provide a more specific version with `-v`.
  - Users can explicitly specify an unspecific version with `-v`.