Savegame: "unused entry" warnings about setting gamestart values
Such values should not get saved at all when game.server.settings_gamestart_valid is not true. Will open a new ticket about that.
But now that stable versions have been saving that information, we need to cleanly load them.
Loading british-isles scenario on S3_1, with --warnings enabled:
...
1: data/scenarios/british-isles.sav.gz: unused entry: settings.set0.gamestart
1: data/scenarios/british-isles.sav.gz: unused entry: settings.set0.gamesetdef
1: data/scenarios/british-isles.sav.gz: unused entry: settings.set1.gamestart
1: data/scenarios/british-isles.sav.gz: unused entry: settings.set1.gamesetdef
...