Backport of subquery optimizations to 5.3.

There are still test failures because of:
- Wrong query results in outer join + semi join
- EXPLAIN output differences

sql/item_cmpfunc.h

@@ -460,13 +460,23 @@ public:
 class Item_func_eq :public Item_bool_rowready_func2
 {
 public:
-  Item_func_eq(Item *a,Item *b) :Item_bool_rowready_func2(a,b) {}
+  Item_func_eq(Item *a,Item *b) :
+    Item_bool_rowready_func2(a,b), in_equality_no(UINT_MAX)
+  {}
   longlong val_int();
   enum Functype functype() const { return EQ_FUNC; }
   enum Functype rev_functype() const { return EQ_FUNC; }
   cond_result eq_cmp_result() const { return COND_TRUE; }
   const char *func_name() const { return "="; }
   Item *negated_item();
+  /* 
+    - If this equality is created from the subquery's IN-equality:
+      number of the item it was created from, e.g. for
+       (a,b) IN (SELECT c,d ...)  a=c will have in_equality_no=0, 
+       and b=d will have in_equality_no=1.
+    - Otherwise, UINT_MAX
+  */
+  uint in_equality_no;
 };
 
 class Item_func_equal :public Item_bool_rowready_func2
@@ -1462,6 +1472,7 @@ public:
   bool add_at_head(Item *item) { return list.push_front(item); }
   void add_at_head(List<Item> *nlist) { list.prepand(nlist); }
   bool fix_fields(THD *, Item **ref);
+  void fix_after_pullout(st_select_lex *new_parent, Item **ref);
 
   enum Type type() const { return COND_ITEM; }
   List<Item>* argument_list() { return &list; }
@@ -1595,6 +1606,9 @@ public:
   virtual void print(String *str, enum_query_type query_type);
   CHARSET_INFO *compare_collation() 
   { return fields.head()->collation.collation; }
+  friend Item *eliminate_item_equal(COND *cond, COND_EQUAL *upper_levels,
+                           Item_equal *item_equal);
+  friend bool setup_sj_materialization(struct st_join_table *tab);
 }; 
 
 class COND_EQUAL: public Sql_alloc