Some errorneous code trimmed


sql/item.cc:
  initialization of the Item_type_holder::orig_item added
sql/item.h:
  No use to call cleanup() in ~Item
  this only calls Item::cleanup()
  
  We should use item->delete_self() instead of 'delete item' now
  
  Code added to restore Item_type_holder::item_type value
sql/item_row.h:
  this cleanup is wrong
sql/item_sum.cc:
  initialization added
sql/item_sum.h:
  Item_xxx& -> Item_xxx*
sql/sql_parse.cc:
  delete item -> item->delete_self()