doesn't need to have it's own recovery mechanism.


sql/item.cc:
  Deployment of centralized Item change registry, step 2: Item_ref 
  doesn't need to have it's own recovery mechanism, so it was simplified.
sql/item.h:
  Deployment of centralized Item change registry, step 2: Item_ref 
  doesn't need to have it's own recovery mechanism, so it was simplified.
sql/item_cmpfunc.cc:
  - Item::split_sum_func now requires THD
  - use THD::register_item_tree_change
sql/item_cmpfunc.h:
  - Item::split_sum_func now requires THD
sql/item_func.cc:
  - Item::split_sum_func now requires THD
  - use THD::register_item_tree_change
sql/item_func.h:
  - Item::split_sum_func now requires THD
sql/item_row.cc:
  - Item::split_sum_func now requires THD
  - use THD::register_item_tree_change
sql/item_row.h:
  - Item::split_sum_func now requires THD
sql/item_strfunc.cc:
  - Item::split_sum_func now requires THD
  - use THD::register_item_tree_change to register changes in the item
    tree
sql/item_strfunc.h:
  - Item::split_sum_func now requires THD
sql/item_subselect.cc:
  - use updated Item_ref constructor
sql/sql_base.cc:
  - Item::split_sum_func now requires THD
sql/sql_select.cc:
  - Item::split_sum_func now requires THD
sql/sql_yacc.yy:
  - use updated Item_ref constructor