Fix updater, compilation, and improve translation

- Fixed the updater thinking a result of UP_TO_DATE meant that the plugin was outdated. This happened because this system is used like this in BigDoors in case the active BD version is a dev-build. However, AE doesn't used dev-builds.
- Fixed resources being placed in the jar twice.
- When the provided text file includes ".txt" in the config, the plugin won't add another ".txt" to the filename (ending up as "filename.txt.txt"). This is a bit more user-friendly.
- Bumped version number to 2.4.13

src/main/java/nl/pim16aap2/armoredElytra/util/ConfigLoader.java

@@ -99,7 +99,7 @@ public class ConfigLoader
             };
         String[] languageFileComment =
             {
-                "Specify a language file to be used. Note that en_US.txt will get regenerated!"
+                "Specify a language file to be used."
             };
         String[] allowMultipleProtectionEnchantmentsComment =
             {

src/main/java/nl/pim16aap2/armoredElytra/util/UpdateManager.java

@@ -1,7 +1,6 @@
 package nl.pim16aap2.armoredElytra.util;
 
 import nl.pim16aap2.armoredElytra.ArmoredElytra;
-import nl.pim16aap2.armoredElytra.util.UpdateChecker.UpdateReason;
 import org.bukkit.scheduler.BukkitRunnable;
 import org.bukkit.scheduler.BukkitTask;
 
@@ -51,15 +50,7 @@ public final class UpdateManager
         if (!checkForUpdates || updater.getLastResult() == null)
             return false;
 
-        // There's a newer version available.
-        if (updater.getLastResult().requiresUpdate())
-            return true;
-
-        // The plugin is "up-to-date", but this is a dev-build, so it must be newer.
-        if (updater.getLastResult().getReason().equals(UpdateReason.UP_TO_DATE))
-            return true;
-
-        return false;
+        return updater.getLastResult().requiresUpdate();
     }
 
     public void checkForUpdates()

src/main/java/nl/pim16aap2/armoredElytra/util/messages/Messages.java

@@ -42,7 +42,10 @@ public class Messages
     public Messages(final ArmoredElytra plugin)
     {
         this.plugin = plugin;
-        textFile = new File(plugin.getDataFolder(), plugin.getConfigLoader().languageFile() + ".txt");
+        final String fileName = plugin.getConfigLoader().languageFile();
+        // Only append .txt if the provided name doesn't already have it.
+        textFile = new File(plugin.getDataFolder(), fileName.endsWith(".txt") ? fileName : (fileName + ".txt"));
+
         if (!textFile.exists())
         {
             plugin.myLogger(Level.WARNING, "Failed to load language file: \"" + textFile +