Add in persistence code for LiquidTank. Using it should protect against liquids that get removed f.e. Closes #395

common/net/minecraftforge/liquids/LiquidTank.java

@@ -1,5 +1,6 @@
 package net.minecraftforge.liquids;
 
+import net.minecraft.nbt.NBTTagCompound;
 import net.minecraft.tileentity.TileEntity;
 
 /**
@@ -149,4 +150,31 @@ public class LiquidTank implements ILiquidTank {
     {
         return LiquidDictionary.findLiquidName(liquid) != null;
     }
+
+
+    public NBTTagCompound writeToNBT(NBTTagCompound nbt)
+    {
+        if (containsValidLiquid())
+        {
+            liquid.writeToNBT(nbt);
+        }
+        else
+        {
+            nbt.setString("emptyTank", "");
+        }
+        return nbt;
+    }
+
+    public LiquidTank readFromNBT(NBTTagCompound nbt)
+    {
+        if (!nbt.hasKey("emptyTank"))
+        {
+            LiquidStack liquid = LiquidStack.loadLiquidStackFromNBT(nbt);
+            if (liquid != null)
+            {
+                setLiquid(liquid);
+            }
+        }
+        return this;
+    }
 }