Predicate LocalFlow::getPostUpdateReverseStep

Holds if a reverse local flow step should be added from the post-update node for e to the post-update node for the result.

This is needed to allow for side-effects on compound expressions to propagate to sub components. For example, in

m(b ? x : y)

we add a reverse flow step from [post] b ? x : y to [post] x and to [post] y, in order for the side-effect of m to reach both x and y.