post review changes 2

sql/event_parse_data.cc:
  don't use "not_used" variable
sql/item_timefunc.cc:
  Item_temporal_func::fix_length_and_dec()
  and other changes
sql/item_timefunc.h:
  introducing Item_timefunc::fix_length_and_dec()
sql/share/errmsg.txt:
  don't say "column X" in the error message that used not only for columns

mysql-test/suite/innodb/r/innodb_mysql.result

@@ -2516,7 +2516,7 @@ INSERT INTO t1 VALUES (0);
 SET SQL_MODE='STRICT_ALL_TABLES';
 CREATE TABLE t2 
 SELECT LEAST((SELECT '' FROM t1),NOW()) FROM `t1`;
-ERROR 22007: Incorrect datetime value: '' for column 'NOW()' at row 1
+ERROR 22007: Truncated incorrect datetime value: ''
 DROP TABLE t1;
 SET SQL_MODE=DEFAULT;
 #