(re-add) Remove tweaker duplicates

Author: simon816

build.gradle

@@ -4,7 +4,7 @@ apply plugin: 'eclipse'
 sourceCompatibility = '1.6'
 targetCompatibility = '1.6'
 
-version = '0.6.3'
+version = '0.7.0'
 
 repositories {
     mavenCentral()

src/main/java/com/simon816/sponge/bootstrap/Bootstrap.java

@@ -207,6 +207,11 @@ public static class PostFMLTweaker extends SimpleTweaker {
 
         @Override
         public void injectIntoClassLoader(LaunchClassLoader classLoader) {
+            // Mixin system already loaded early so don't load twice
+            @SuppressWarnings("unchecked")
+            List<String> tweakClasses = (List<String>) Launch.blackboard.get("TweakClasses");
+            while (tweakClasses.remove("org.spongepowered.asm.launch.MixinTweaker")) {
+            }
             // Fix location of jar file
             try {
                 Field fPlugins = CoreModManager.class.getDeclaredField("loadPlugins");