check_equality() finds equalities among field items. It checks input items
to be Item_fields thus skipping view's fields, which are represented by
Item_direct_view_ref. Because of this index wasn't applied in all cases
it can be.

To fix this problem check_equality() now takes real item of
Item_direct_view_ref, except outer view refs (with depended_from set).


sql/sql_select.cc:
  Fix bug #13327 VIEW performs index scan
   For proper views fields handling check_equality() now takes real item from Item_direct_view_ref, with exception of outer view refs.
mysql-test/r/view.result:
  Test case for bug#13327 VIEW performs index scan
mysql-test/t/view.test:
  Test case for bug#13327 VIEW performs index scan