Corrected the code of the recent patch that had changed the base

class for Item_func_xor. Added the implementation of the
subst_argument_checker virtual method that the objects of this 
class used to use before the patch.
Reverted the previous result changes in sunselect_sj and
subselect_sj_jcl6.
  

mysql-test/r/subselect_sj.result

@@ -968,7 +968,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	18	100.00	
 1	PRIMARY	t1	ref	varchar_key	varchar_key	3	test.t2.varchar_nokey	2	100.00	Using where; FirstMatch(t2)
 Warnings:
-Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_key` = `test`.`t2`.`varchar_nokey`) and (`test`.`t1`.`varchar_nokey` = `test`.`t2`.`varchar_nokey`) and ((`test`.`t1`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
+Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_key` = `test`.`t2`.`varchar_nokey`) and (`test`.`t1`.`varchar_nokey` = `test`.`t2`.`varchar_nokey`) and ((`test`.`t2`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
 SELECT varchar_nokey
 FROM t2  
 WHERE ( `varchar_nokey`  , `varchar_nokey`  )  IN (  

mysql-test/r/subselect_sj_jcl6.result

@@ -978,7 +978,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	18	100.00	
 1	PRIMARY	t1	ref	varchar_key	varchar_key	3	test.t2.varchar_nokey	2	100.00	Using where; FirstMatch(t2); Using join buffer (flat, BKA join); Key-ordered Rowid-ordered scan
 Warnings:
-Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_key` = `test`.`t2`.`varchar_nokey`) and (`test`.`t1`.`varchar_nokey` = `test`.`t2`.`varchar_nokey`) and ((`test`.`t1`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
+Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_key` = `test`.`t2`.`varchar_nokey`) and (`test`.`t1`.`varchar_nokey` = `test`.`t2`.`varchar_nokey`) and ((`test`.`t2`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
 SELECT varchar_nokey
 FROM t2  
 WHERE ( `varchar_nokey`  , `varchar_nokey`  )  IN (  

sql/item_cmpfunc.h

@@ -405,6 +405,10 @@ public:
   longlong val_int();
   void top_level_item() {}
   Item *neg_transformer(THD *thd);
+  bool subst_argument_checker(uchar **arg)
+  {
+    return (*arg != NULL);     
+  }
 };
 
 class Item_func_not :public Item_bool_func