Savecompat to 3.1 format: Add setting gamesetdef values
https://www.hostedredmine.com/issues/692373 adds 'gamesetdef' value to settings in the savegame. The code reading the values from the savegame survives lack of that value, but we should still add the value in compat_load_030100()
https://www.hostedredmine.com/issues/692373 adds 'gamesetdef' value to settings in the savegame. The code reading the values from the savegame survives lack of that value, but we should still add the value in compat_load_030100()