PS and SP made compatible in mechanism used for preparing query for rexecutions (Bug #2266)

mysql-test/r/sp.result:
  test suite for Bug #2266
mysql-test/t/sp.test:
  test suite for Bug #2266
sql/item_subselect.cc:
  made ancestor for Statement (Item_arena)
sql/item_subselect.h:
  made ancestor for Statement (Item_arena)
sql/item_sum.cc:
  made ancestor for Statement (Item_arena)
sql/item_sum.h:
  made ancestor for Statement (Item_arena)
sql/mysql_priv.h:
  reset_stmt_for_execute use PS and SP
sql/sp_head.cc:
  sp_head use Item_arena as ancestor to be PS cleunup compatible
  SP use PS storing/restoring/cleanup mechanisms
  cleanup() of SP Items added
  Items created in temporary memory pool during SP execution saved for normal freeing after SP execution
sql/sp_head.h:
  sp_head use Item_arena
sql/sql_base.cc:
  made ancestor for Statement (Item_arena)
  results of wild_setup made permanent
  setup_conds make natural joins expanding only once and store results in PS/SP memory
sql/sql_class.cc:
  made ancestor for Statement (Item_arena)
sql/sql_class.h:
  made ancestor for Statement (Item_arena)
  method to detect PS preparation added
sql/sql_delete.cc:
  storing where for DELETE and mark first execution
sql/sql_derived.cc:
  use method
sql/sql_insert.cc:
  mark first execution for INSERT
sql/sql_lex.cc:
  flags to correctly make transformations of query and storing them in memory of PS/SP
  made ancestor for Statement (Item_arena)
sql/sql_lex.h:
  reved variable od SP ol saving data
  flags to correctly make transformations of query and storing them in memory of PS/SP
sql/sql_parse.cc:
  cleunup unit for any query
sql/sql_prepare.cc:
  made ancestor for Statement (Item_arena)
  storing where moved to preparation
  changed interface of reset_stmt_for_execute to use it is SP
  do not restore where/order by/group by before first execution (but tables and unit can be chenged without execution and should be prepared (subqueries executes on demand))
sql/sql_select.cc:
  storing where for SELECT/multi-DELETE/... and mark first execution
sql/sql_union.cc:
  made ancestor for Statement (Item_arena)
sql/sql_update.cc:
  storing where for UPDATE and mark first execution

sql/sp_head.h

@@ -70,7 +70,7 @@ sp_name *
 sp_name_current_db_new(THD *thd, LEX_STRING name);
 
 
-class sp_head : public Sql_alloc
+class sp_head :private Item_arena
 {
   sp_head(const sp_head &);	/* Prevent use of these */
   void operator=(sp_head &);
@@ -206,9 +206,7 @@ public:
 
 private:
 
-  MEM_ROOT m_mem_root;		// My own mem_root
   MEM_ROOT m_thd_root;		// Temp. store for thd's mem_root
-  Item *m_free_list;		// Where the items go
   THD *m_thd;			// Set if we have reset mem_root
   char *m_thd_db;		// Original thd->db pointer