Feature request: Add a licencing-change check to the update process.

To make sure that we're respectful of software licenses and handling their integration correctly, I'd like to ask that our updater tool include a verification step when licenses change. It should be a rare event - it has been historically, at least - so I think the right thing here is that if a license is changed:

• the tool should by default fail and provide an error message saying a human should verify the update because of licensing changes in [whatever file], and
• an explicit "permit-new-license" option be available, that permits license changes to go ahead.

There are other approaches we could take here but in my opinion this is a place that merits manual intervention, so what we want is code that's as dumb as possible and responsible people making explicit decisions.

Start by tracing the updater tool's update process and its option parsing, then inspect how it currently reports verification failures. Determine where license changes can be detected and how the affected file is identified. Done means changed licenses fail by default with a human-review message, while the explicit "permit-new-license" option allows the update to proceed.