Fixed spec for sum() in a predicate
Fixed spec for sum() in a predicate

The return value of sum() should be used as a NodeSet index, not merely
just a truthy value.

ttasanen/oga,ttasanen/oga,ttasanen/oga,ttasanen/oga,YorickPeterse/oga,YorickPeterse/oga,ttasanen/oga,YorickPeterse/oga,YorickPeterse/oga,YorickPeterse/oga