Adding support for buying nation specific units in Europe.

src/net/sf/freecol/client/gui/panel/PurchasePanel.java

@@ -39,6 +39,6 @@ public final class PurchasePanel extends NewUnitPanel {
         super(freeColClient, new MigLayout("wrap 2", "[sg]", ""),
             Messages.message("purchasePanel.clickOn"),
             freeColClient.getGame().getSpecification()
-                .getUnitTypesPurchasedInEurope());
+                .getUnitTypesPurchasedInEurope(freeColClient.getMyPlayer()));
     }
 }

src/net/sf/freecol/client/gui/panel/TrainPanel.java

@@ -39,6 +39,6 @@ public final class TrainPanel extends NewUnitPanel {
         super(freeColClient, new MigLayout("wrap 3", "[sg]", ""),
             Messages.message("trainPanel.clickOn"),
             freeColClient.getGame().getSpecification()
-                .getUnitTypesTrainedInEurope());
+                .getUnitTypesTrainedInEurope(freeColClient.getMyPlayer()));
     }
 }

src/net/sf/freecol/common/model/Specification.java

@@ -1933,19 +1933,25 @@ public final class Specification implements OptionContainer {
     /**
      * Gets the unit types that can be trained in Europe.
      *
+     * @param player The player that want to purchase the unit.
      * @return A list of Europe-trainable {@code UnitType}s.
      */
-    public List<UnitType> getUnitTypesTrainedInEurope() {
-        return unitTypesTrainedInEurope;
+    public List<UnitType> getUnitTypesTrainedInEurope(Player player) {
+        return unitTypesTrainedInEurope.stream()
+                .filter(type -> type.isAvailableTo(player))
+                .collect(Collectors.toList());
     }
-
+    
     /**
-     * Get the unit types that can be purchased in Europe.
+     * Get the unit types that can be purchased in Europe for a given player.
      *
+     * @param player The player that want to purchase the unit.
      * @return A list of Europe-purchasable {@code UnitType}s.
      */
-    public List<UnitType> getUnitTypesPurchasedInEurope() {
-        return unitTypesPurchasedInEurope;
+    public List<UnitType> getUnitTypesPurchasedInEurope(Player player) {
+        return unitTypesPurchasedInEurope.stream()
+                .filter(type -> type.isAvailableTo(player))
+                .collect(Collectors.toList());
     }
 
     /**

src/net/sf/freecol/server/control/InGameController.java

@@ -3802,6 +3802,9 @@ public final class InGameController extends Controller {
                 + serverPlayer.getGold() + " < " + price
                 + ") to train " + type);
         }
+        if (!type.isAvailableTo(serverPlayer)) {
+            return serverPlayer.clientError("Unit type is not available for the player.");
+        }
 
         final Game game = getGame();
         final Specification spec = game.getSpecification();