[bombela]

And before any major change, add a `--v2` for early adopters and `--v1` as default. Nobody should notice anything on `--v1`, any regression must be fixed imediately. Flip `--v2` as default, leaving `--v1` for the unforseen. Until you can finally get rid of them.

This helps being as invisible as possible.

[rmunn]

Excellent idea; it's good practice to do that with APIs, so why not with command-line tools as well?