correct eq() method for Item_param (BUG#4233)

mysql-test/r/ps.result:
  eq() for parameters test
mysql-test/t/ps.test:
  eq() for parameters test
sql/item.h:
  correct eq() method for Item_param

mysql-test/r/ps.result

@@ -191,4 +191,21 @@ execute stmt1 using @arg00;
 select m from t1;
 m
 1
+deallocate prepare stmt1;
+drop table t1;
+create table t1 (id int(10) unsigned NOT NULL default '0',
+name varchar(64) NOT NULL default '',
+PRIMARY KEY  (id), UNIQUE KEY `name` (`name`));
+insert into t1 values (1,'1'),(2,'2'),(3,'3'),(4,'4'),(5,'5'),(6,'6'),(7,'7');
+prepare stmt1 from 'select name from t1 where id=? or id=?';
+set @id1=1,@id2=6;
+execute stmt1 using @id1, @id2;
+name
+1
+6
+select name from t1 where id=1 or id=6;
+name
+1
+6
+deallocate prepare stmt1;
 drop table t1;

mysql-test/t/ps.test

@@ -178,4 +178,19 @@ drop table t1;
 prepare stmt1 from ' create table t1 (m int) as select ? as m ' ;
 execute stmt1 using @arg00;
 select m from t1;
+deallocate prepare stmt1;
+drop table t1;
+
+#
+# eq() for parameters
+#
+create table t1 (id int(10) unsigned NOT NULL default '0',
+                 name varchar(64) NOT NULL default '',
+                 PRIMARY KEY  (id), UNIQUE KEY `name` (`name`));
+insert into t1 values (1,'1'),(2,'2'),(3,'3'),(4,'4'),(5,'5'),(6,'6'),(7,'7');
+prepare stmt1 from 'select name from t1 where id=? or id=?';
+set @id1=1,@id2=6;
+execute stmt1 using @id1, @id2;
+select name from t1 where id=1 or id=6;
+deallocate prepare stmt1;
 drop table t1;

sql/item.h

@@ -525,6 +525,8 @@ class Item_param :public Item
   virtual table_map used_tables() const
   { return state != NO_VALUE ? (table_map)0 : PARAM_TABLE_BIT; }
   void print(String *str) { str->append('?'); }
+  /* parameter never equal to other parameter of other item */
+  bool eq(const Item *item, bool binary_cmp) const { return 0; }
 };
 
 class Item_int :public Item_num