with older FreeBSD versions:
- Add -V option to 'geli init' to specify version number. If no -V is given
the most recent version is used.
- If -V is given don't allow to use features not supported by this version.
- Print version in 'geli list' output.
- Update manual page and add table describing which GELI version is
supported by which FreeBSD version, so one can use it when preparing GELI
device for older FreeBSD version.
Inspired by: Garrett Cooper <yanegomi@gmail.com>
MFC after: 3 days
1f8c92e6fa