Here i added Item_*::cleanup() functions,
removed a lot of ~Item_*'s,
added code to restore order_list and group_list


sql/item.cc:
  cleanups methods implemented
  Item_ref constructors changed
sql/item.h:
  cleanups declared
  Item_ref constructors changed
  some ~Item_* deleted
sql/item_cmpfunc.cc:
  new Item_ref format
sql/item_cmpfunc.h:
  saving/restoring of the original arguments added to
  eq and equal functions
sql/item_func.cc:
  New Item_ref format
sql/item_func.h:
  destructors removed/changed to 'cleanup()'
sql/item_row.cc:
  New Item_ref format
sql/item_row.h:
  ~Item_row -> cleanup()
sql/item_strfunc.cc:
  new Item_ref format
sql/item_strfunc.h:
  destructors removed
sql/item_subselect.cc:
  Item_subselect implementation,
  new Item_ref() format
sql/item_subselect.h:
  cleanups for subselects declared
sql/item_sum.cc:
  cleanups implementations
sql/item_sum.h:
  cleanups declarations
  destructors removed
sql/mysql_priv.h:
  free_items, cleanup_items exported
sql/sql_prepare.cc:
  cleanup_items, free_items calls added
  stmt->query_id= thd->query_id restored
  cleanup procedures for group_list and order_list added
sql/sql_yacc.yy:
  New Item_ref() format