Add dummy /testfor command in Bukkit. Addresses BUKKIT-3813

This command only functions in command blocks so the bukkit command for it
simply spits out an error message.

src/main/java/org/bukkit/command/SimpleCommandMap.java

@@ -55,6 +55,7 @@ public class SimpleCommandMap implements CommandMap {
         fallbackCommands.add(new ClearCommand());
         fallbackCommands.add(new GameRuleCommand());
         fallbackCommands.add(new EnchantCommand());
+        fallbackCommands.add(new TestForCommand());
     }
 
     public SimpleCommandMap(final Server server) {

src/main/java/org/bukkit/command/defaults/TestForCommand.java

@@ -0,0 +1,26 @@
+package org.bukkit.command.defaults;
+
+import org.bukkit.Bukkit;
+import org.bukkit.ChatColor;
+import org.bukkit.command.CommandSender;
+
+public class TestForCommand extends VanillaCommand {
+    public TestForCommand() {
+        super("testfor");
+        this.description = "Tests whether a specifed player is online";
+        this.usageMessage = "/testfor <player>";
+        this.setPermission("bukkit.command.testfor");
+    }
+
+    @Override
+    public boolean execute(CommandSender sender, String currentAlias, String[] args) {
+        if (!testPermission(sender)) return true;
+        if (args.length < 1)  {
+            sender.sendMessage(ChatColor.RED + "Usage: " + usageMessage);
+            return false;
+        }
+
+        sender.sendMessage(ChatColor.RED + "/testfor is only usable by commandblocks with analog output.");
+        return true;
+    }
+}