Ignore block functions for skulls on BlockPlace. Fixes BUKKIT-3495

Skulls don't normally get block data applied to them, so we shouldn't
apply it either.

src/main/java/net/minecraft/server/ItemBlock.java

@@ -105,7 +105,8 @@ public class ItemBlock extends Item {
 
         world.update(x, y, z, newId);
 
-        if (block != null) {
+        // Skulls don't get block data applied to them
+        if (block != null && block != Block.SKULL) {
             block.postPlace(world, x, y, z, entityhuman);
             block.postPlace(world, x, y, z, newData);