Let stateful tactics try all decompositions.
This problem has been reported by Léon Gondelman. Before, when using, for example wp_alloc, in an expression like: ref (ref v) It would apply `tac_wp_alloc` to the outermost ref, after which it fails to establish that the argument `ref v` is a value. In this commit, other evaluation positions will be tried whenever it turn out that the argument of the construct is not a value. The same applies to store/cas/... I have implemented this by making use of the new `IntoVal` class.