hmm, this missing file might be helpful to have on GitHub as well

src/com/wimbli/WorldBorder/BorderCheckTask.java

@@ -0,0 +1,83 @@
+package com.wimbli.WorldBorder;
+
+import java.util.Iterator;
+
+import org.bukkit.ChatColor;
+import org.bukkit.entity.Player;
+import org.bukkit.Location;
+import org.bukkit.Server;
+import org.bukkit.util.Vector;
+import org.bukkit.World;
+
+public class BorderCheckTask implements Runnable
+{
+	Server server;
+
+	public BorderCheckTask(Server theServer)
+	{
+		this.server = theServer;
+	}
+
+	public void run()
+	{
+		if (Config.movedPlayers.isEmpty())
+			return;
+
+		for (Iterator<String> p = Config.movedPlayers.iterator(); p.hasNext();)
+		{
+			String playerName = p.next();
+			Player player = server.getPlayer(playerName);
+			p.remove();
+
+			if (player == null || !player.isOnline()) continue;
+
+			Location loc = player.getLocation();
+			if (loc == null) continue;
+			World world = loc.getWorld();
+			if (world == null) continue;
+			BorderData border = Config.Border(world.getName());
+			if (border == null) continue;
+
+			if (border.insideBorder(loc.getX(), loc.getZ(), Config.ShapeRound()))
+				continue;
+
+			Location newLoc = newLocation(player, loc, border);
+
+			if (!player.isInsideVehicle())
+				player.teleport(newLoc);
+			else
+			{	// vehicles need to be offset vertically and have velocity stopped
+				double vertOffset = player.getVehicle().getLocation().getY() - loc.getY();
+				newLoc.setY(newLoc.getY() + vertOffset);
+				player.getVehicle().setVelocity(new Vector(0, 0, 0));
+				player.getVehicle().teleport(newLoc);
+			}
+		}
+	}
+
+	private static Location newLocation(Player player, Location loc, BorderData border)
+	{
+		if (Config.Debug())
+		{
+			Config.LogWarn("Border crossing. Border " + border.toString());
+			Config.LogWarn("Player position X: " + Config.coord.format(loc.getX()) + " Y: " + Config.coord.format(loc.getY()) + " Z: " + Config.coord.format(loc.getZ()));
+		}
+
+		Location newLoc = border.correctedPosition(loc, Config.ShapeRound());
+
+		// it's remotely possible (such as in the Nether) a suitable location isn't available, in which case...
+		if (newLoc == null)
+		{
+			if (Config.Debug())
+				Config.LogWarn("Target new location unviable, using spawn.");
+			newLoc = player.getServer().getWorlds().get(0).getSpawnLocation();
+		}
+
+		if (Config.Debug())
+			Config.LogWarn("New position X: " + Config.coord.format(newLoc.getX()) + " Y: " + Config.coord.format(newLoc.getY()) + " Z: " + Config.coord.format(newLoc.getZ()));
+
+		player.sendMessage(ChatColor.RED + Config.Message());
+
+		return newLoc;
+	}
+}