Added test case for bug #11867.
  Fixed results for two existing test cases.
subselect.test:
  Added test case for bug #11867.
item_subselect.cc:
  Fixed bug #11867.
  Added missing code in Item_in_subselect::row_value_transformer
  that caused problems for queries with
  ROW(elems) IN (SELECT DISTINCT cols FROM ...).


sql/item_subselect.cc:
  Fixed bug #11867.
  Added missing code in Item_in_subselect::row_value_transformer
  that caused problems for queries with
  ROW(elems) IN (SELECT DISTINCT cols FROM ...).
mysql-test/t/subselect.test:
  Added test case for bug #11867.
mysql-test/r/subselect.result:
  Added test case for bug #11867.
  Fixed results for two existing test cases.