A combination of forall and invalid is syntax panics the syntax macro

[utaal]

Minimized to

        use vstd::seq::*;

        enum Alternative {
            Yes,
            No,
        }

        spec fn is_test_original(s: Seq<Option<Alternative>>) -> bool {
            &&& forall|b:nat| b < s.len() ==> s[b as int] is Some(Alternative::Yes)
        }

        spec fn is_test_minimal(s: Seq<Option<Alternative>>) -> bool {
            &&& forall|b:nat| s[b as int] is Some(Alternative::Yes)
        }

---

• un-ignore test added in 5fd2be1a