message: Correct pedia references to Astronomy to Exploration
diff: [ICON_BULLET]Cities of a vassalized civilization can keep control of the first ring around its cities, unless it's also the first ring of a master's city
  [ICON_BULLET]AI civilizations become more unstable if they survive ahistorically long
  [ICON_BULLET]The American conqueror event automatically leads to war
  -[ICON_BULLET]It's impossible to vassalize far away civilizations until the discovery of Astronomy
  -[ICON_BULLET]It's impossible to train settlers on other continents than your capital's until the discovery of Astronomy
  +[ICON_BULLET]It's impossible to vassalize far away civilizations until the discovery of Exploration
  +[ICON_BULLET]It's impossible to train settlers on other continents than your capital's until the discovery of Exploration
  [ICON_BULLET]AI Mongols get additional armies to attack Russia and the Middle East
  [ICON_BULLET]Pagan Temples can only be built in cities without religions (this does not apply to unique buildings that replace Pagan Temples)
  [ICON_BULLET]Religion spread to a city turns Pagan Temples into temples of the new religion
  