CAS methods but without dests

[imacks]

This is a feature request to use CAS functions without having to supply dests. In a lot of use cases, I just want to check the [applied] field and error, so something like Query.ExecCAS() (bool, error) would work nicely. I can pass in a slice of nils, but I'm not seeing a way to get the number of columns returned without being able to access Iter.