The problem was that optimizer removes some outer references (it they are
constant for example) and the list of outer items built during prepare phase is
not actual during execution phase when we need it as the cache parameters.
First solution was use pointer on pointer on outer reference Item and
initialize temporary table on demand. This solved most problem except case
when optimiser also reduce Item which contains outer references ('OR' in
this bug test suite).

The solution is to build the list of outer reference items on execution
phase (after optimization) on demand (just before temporary table creation)
by walking Item tree and finding outer references among Item_ident
(Item_field/Item_ref) and Item_sum items.

Removed depends_on list (because it is not neede any mnore for the cache, in the place where it was used it replaced with upper_refs).

Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references (or other expression parameters in future).

mysql-test/r/subselect_cache.result:
  A new test added.
mysql-test/r/subselect_scache.result:
  Changes in creating the cache and its paremeters order or adding arguments of aggregate function (which is a parameter also, but this has no influence on the result).
mysql-test/t/subselect_cache.test:
  Added a new test.
sql/item.cc:
  depends_on removed.
  
  Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
  
  Item_cache_wrapper collect parameters befor initialization of its cache.
sql/item.h:
  depends_on removed.
  
  Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
sql/item_cmpfunc.cc:
  depends_on removed.
  
  Added processor (collect_outer_ref_processor) to collect outer references.
sql/item_cmpfunc.h:
  Added processor (collect_outer_ref_processor) to collect outer references.
sql/item_subselect.cc:
  depends_on removed.
  Added processor get_cache_parameters() method to collect outer references.
sql/item_subselect.h:
  depends_on removed.
  Added processor get_cache_parameters() method to collect outer references.
sql/item_sum.cc:
  Added processor (collect_outer_ref_processor) method to collect outer references.
sql/item_sum.h:
  Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
sql/opt_range.cc:
  depends_on removed.
sql/sql_base.cc:
  depends_on removed.
sql/sql_class.h:
  New iterator added.
sql/sql_expression_cache.cc:
  Build of list of items resolved in outer query done just before creating expression cache on the first execution of the subquery which removes influence of optimizer removing items (all optimization already done).
sql/sql_expression_cache.h:
  Build of list of items resolved in outer query done just before creating expression cache on the first execution of the subquery which removes influence of optimizer removing items (all optimization already done).
sql/sql_lex.cc:
  depends_on removed.
sql/sql_lex.h:
  depends_on removed.
sql/sql_list.h:
  Added add_unique method to add only unique elements to the list.
sql/sql_select.cc:
  Support of new Item list added.
sql/sql_select.h:
  Support of new Item list added.