Fields of view represented by Item_direct_view_ref. When complex expression
such as if(sum()>...,...) is splited in simpler parts by refs was ignored.
Beside this direct ref doesn't use it's result_field and thus can't store
it's result in tmp table which is needed for sum() ... group.
All this results in reported bug.

Item::split_sum_func2() now converts Item_direct_view_ref to Item_ref to
make fields from view being storable in tmp table.


sql/item.h:
  Fix bug #12922 if(sum(),...) with group from view returns wrong results
  Added function ref_type() to distinguish Item_ref subclasses
sql/item.cc:
  Fix bug #12922 if(sum(),...) with group from view returns wrong results
   Item::split_sum_func2() now converts Item_direct_view_ref to Item_ref to make fields from view being storable in tmp table.
mysql-test/t/view.test:
  Test case for bug#12922 if(sum(),...) with group from view returns wrong results
mysql-test/r/view.result:
  Test case for bug#12922 if(sum(),...) with group from view returns wrong results