The patch broke expressions like CAST(1.0e+300 AS SIGNED INT)
in binary protocol, e.g.:
  mtr --ps cast

Short real numbers like 1.0e+300 can return huge values,
so using args[0]->max_length is not reliable to choose properly the result
type for Item_func_signed and Item_func_unsigned (between INT and BIGINT).

Setting Item_[un]signed_typecast::max_length to MAX_BIGINT_WIDTH
when doing CAST from FLOAT/DOUBLE, to force type_handler() return
&type_handler_longlong rather than &type_handler_long.