Make SlotItemHandler override Slot.getSlotStackLimit. Closes #3497

Make Container.mergeItemStack respect target slot's max size when slot is non-empty. Closes #3498
Fix Shift clicking in Beacons with stacked items when fuel slot is empty.

src/main/java/net/minecraftforge/items/SlotItemHandler.java

@@ -87,6 +87,12 @@ public class SlotItemHandler extends Slot
 
     }
 
+    @Override
+    public int getSlotStackLimit()
+    {
+        return this.itemHandler.getSlotLimit(this.index);
+    }
+
     @Override
     public int getItemStackLimit(@Nonnull ItemStack stack)
     {