message: Maya Ball Court requires Calendar and is cheaper to build
diff: <Strategy>TXT_KEY_BUILDING_MAYAN_BALL_COURT_STRATEGY</Strategy>
  <Advisor>ADVISOR_ECONOMY</Advisor>
  <ArtDefineTag>ART_DEF_BUILDING_MAYAN_BALL_COURT</ArtDefineTag>
  - <PrereqTech>TECH_ENGINEERING</PrereqTech>
  - <iCost>80</iCost>
  + <PrereqTech>TECH_CALENDAR</PrereqTech>
  + <iCost>60</iCost>
  <iAdvancedStartCost>100</iAdvancedStartCost>
  <iMinAreaSize>-1</iMinAreaSize>
  <iConquestProb>66</iConquestProb>
  - <iHappiness>3</iHappiness>
  + <iHappiness>1</iHappiness>
  <iAsset>5</iAsset>
  <fVisibilityPriority>1.0</fVisibilityPriority>
  <CommerceHappinesses>
  