RelTy for CBind is no longer a maybe.

Also renamed the maybes from ty to mbTy.
Removing chunk of constraint solving we wont need

This is and will most likely stay dead.
Imroving code ever so slightly in relevance.

Fixing a potential bug in the propagation of envronments and in the
generalization of types in lets.
Fixing the update variable func in relevance.
Fixing a bug in the propagating of env in let.

This rather small change stopped my code from properly unifying let bound
variables with the result of their definition in all three types of lets.