WL#3527 : inspected a 5.1 covarage report

sql/item.cc:
  WL#3527 : inspected a covarage report

sql/item.cc

@@ -3907,7 +3907,9 @@ bool Item_field::fix_fields(THD *thd, Item **reference)
       {
         /* First usage of column */
         table->used_fields++;                     // Used to optimize loops
+        /* purecov: begin inspected */
         table->covering_keys.intersect(field->part_of_key);
+        /* purecov: end */
       }
     }
   }