Reinitalize statistics information on Mapping changes.

Fixes mismatched stats to item/block ids. And auto registers stats for modded items.
Closes #2454

src/main/java/net/minecraftforge/common/ForgeModContainer.java

@@ -20,6 +20,7 @@ import java.util.Map;
 
 import net.minecraft.nbt.NBTBase;
 import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.stats.StatList;
 import net.minecraft.world.storage.SaveHandler;
 import net.minecraft.world.storage.WorldInfo;
 import net.minecraftforge.classloading.FMLForgePlugin;
@@ -350,6 +351,12 @@ public class ForgeModContainer extends DummyModContainer implements WorldAccessC
         }
     }
 
+    @Subscribe
+    public void mappingChange(FMLModIdMappingEvent evt)
+    {
+        StatList.reinit();
+    }
+
     @Subscribe
     public void postInit(FMLPostInitializationEvent evt)
     {