message: Republic also affects Slave Plantations
diff: <iYield>-1</iYield>
  </ImprovementYields>
  </ImprovementYieldChange>
  + <ImprovementYieldChange>
  + <ImprovementType>IMPROVEMENT_SLAVE_PLANTATION</ImprovementType>
  + <ImprovementYields>
  + <iYield>-1</iYield>
  + </ImprovementYields>
  + </ImprovementYieldChange>
  <ImprovementYieldChange>
  <ImprovementType>IMPROVEMENT_COTTAGE</ImprovementType>
  <ImprovementYields>
  