Fixes #2433: Readded decorative slabs.

src/main/java/appeng/bootstrap/IBlockBuilder.java

@@ -45,6 +45,11 @@ public interface IBlockBuilder
 
 	IBlockBuilder rendering( BlockRenderingCustomizer callback );
 
+	/**
+	 * Don't register an item for this block.
+	 */
+	IBlockBuilder disableItem();
+
 	/**
 	 * Forces this block's item to uses a custom model, instead of using the default block state as the item model.
 	 * The model has the same name as the registry name.