Ensure that the preferred version has the right type.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Ensure CSV downgrades don't corrupt data.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Allow command-line upgrades and downgrades.

This allows for easier testing of conversions.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>