A bug about casting to supertype

[LuKuangChen]

This program cannot be compiled with the latest compiler in the master branch.

(: (tuple 42 #f) (Tuple Int))

[akuhlens]

Here is another program that we should make sure that the type-checker and runtime rejects.

(ann (vector 1 (tuple 1 #f)) (Vect (Tuple Int)))

Here the contents of the vector have to be invariant with respect to the subtyping relationship.