After adding an index the <VARBINARY> IN (SELECT <BINARY> ...)
clause returned a wrong result: the VARBINARY value was illegally padded
with zero bytes to the length of the BINARY column for the index search.
(<VARBINARY>, ...) IN (SELECT <BINARY>, ... ) clauses are affected too.


sql/item.cc:
  Fixed bug #28076.
  The Item_cache_str::save_in_field method has been overloaded
  to check cached values for an illegal padding before the saving
  into a field.
sql/item.h:
  Fixed bug #28076.
  The Item_cache_str::is_varbinary flag has been added and the
  Item_cache_str::save_in_field method has been overloaded to prevent
  cached values from an illegal padding when saving in fields.
  The signature of the Item_cache::get_cache method has been
  changed to accept pointers to Item instead of Item_result
  values.
sql/item_cmpfunc.cc:
  Fixed bug #28076.
  The Item_in_optimizer::fix_left method has been modified to
  to call Item_cache::get_cache in a new manner.
sql/item_subselect.cc:
  Fixed bug #28076.
  The subselect_indexsubquery_engine::exec method has been
  modified to take into account field conversion errors
  (copy&paste from subselect_uniquesubquery_engine::exec).
sql/sp_rcontext.cc:
  Fixed bug #28076.
  The sp_rcontext::create_case_expr_holder method has been
  modified to call Item_cache::get_cache in a new manner.
sql/sp_rcontext.h:
  Fixed bug #28076.
  The sp_rcontext::create_case_expr_holder method signature
  has been modified to pass Item pointers to the
  Item_cache::get_cache method.
sql/sql_class.cc:
  Fixed bug #28076.
  The select_max_min_finder_subselect::send_data method has been
  modified to call Item_cache::get_cache in a new manner.
mysql-test/t/subselect.test:
  Added test case for bug #28076.
mysql-test/r/subselect.result:
  Added test case for bug #28076.