test_if_order_by_key() expected only Item_fields to be in order->item, thus
failing to find available index on view's field, which results in reported
error.

Now test_if_order_by_key() calls order->item->real_item() to get field for
choosing index.


sql/sql_select.cc:
  Fix bug #14816 test_if_order_by_key() expected only Item_fields.
  Make test_if_order_by_key() use real_item() to get field.
mysql-test/r/view.result:
  Test case for bug#14816 test_if_order_by_key() expected only Item_fields.
mysql-test/t/view.test:
  Test case for bug#14816 test_if_order_by_key() expected only Item_fields.