memory leak fixed

mysql-test/r/update.result

@@ -109,6 +109,6 @@ update t1 set b=4 where a=1 order by b desc limit 1;
 select * from t1;
 a	b
 1	4
-1	4
 1	2
+1	4
 drop table t1;

sql/sql_update.cc

@@ -335,5 +335,6 @@ int mysql_update(THD *thd,
     DBUG_PRINT("info",("%d records updated",updated));
   }
   thd->count_cuted_fields=0;			/* calc cuted fields */
+  free_io_cache(table);
   DBUG_RETURN(0);
 }