1. Adding the forgotten "SET sql_mode=STRICT_ALL_TABLES" into the test.
2. STRICT_ALL_TABLES revealed that CAST(0xFFFFFFFF AS SIGNED),
   e.g. with a hex number with 8 hex digits, did not work well.
   Fixing Item_func_unsigned::create_tmp_field() and
   Item_func_unsigned::create_field_for_create_select() to handle
   this corner case.