Test command permissions before running them.

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

@@ -19,6 +19,7 @@ public class DefaultGameModeCommand extends VanillaCommand {
 
     @Override
     public boolean execute(CommandSender sender, String commandLabel, String[] args) {
+        if (!testPermission(sender)) return true;
         if (args.length == 0) {
             sender.sendMessage("Useage: " + usageMessage);
             return false;

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

@@ -14,6 +14,7 @@ public class SeedCommand extends VanillaCommand {
 
     @Override
     public boolean execute(CommandSender sender, String commandLabel, String[] args) {
+        if (!testPermission(sender)) return true;
         long seed;
         if (sender instanceof Player) {
             seed = ((Player) sender).getWorld().getSeed();