message: Vassal states require Contract
diff: <iPower>3</iPower>
  <bTrade>1</bTrade>
  <bGoodyTech>0</bGoodyTech>
  + <bVassalTrading>1</bVassalTrading>
  <iGridX>4</iGridX>
  <iGridY>7</iGridY>
  <Flavors>
  <iPower>3</iPower>
  <bTrade>1</bTrade>
  <bGoodyTech>0</bGoodyTech>
  - <bVassalTrading>1</bVassalTrading>
  <iGridX>7</iGridX>
  <iGridY>1</iGridY>
  <Flavors>
  