Added minecart classes and World.spawn*Minecart(). Minecart.getPassenger() is still a stub that needs to be implemented (due to of a need of a MC entity -> CraftBukkit entity lookup) and StorageMinecart.getInventory() is waiting on the implementation of inventory.

src/main/java/org/bukkit/craftbukkit/CraftVehicle.java

@@ -0,0 +1,16 @@
+package org.bukkit.craftbukkit;
+
+import net.minecraft.server.Entity;
+
+import org.bukkit.Vehicle;
+
+/**
+ * A vehicle.
+ * 
+ * @author sk89q
+ */
+public abstract class CraftVehicle extends CraftEntity implements Vehicle {
+    public CraftVehicle(CraftServer server, Entity entity) {
+        super(server, entity);
+    }
+}