change, and perform it (the new Item changes registry).


sql/item.cc:
  A small simplification: perform two actions at once, register a
  change, and perform it.
sql/item_cmpfunc.cc:
  register_item_tree_change -> change_item_tree
sql/item_func.cc:
  register_item_tree_change -> change_item_tree
sql/item_row.cc:
  register_item_tree_change -> change_item_tree
sql/item_strfunc.cc:
  register_item_tree_change -> change_item_tree
sql/sql_class.h:
  register_item_tree_change -> change_item_tree
sql/sql_select.cc:
  register_item_tree_change -> change_item_tree