enhancement: inference for generic functions

[crusso]

At first I was surprised this doesn't work, but I think it's because we never implemented checking for proper generic, untyped lambdas

let c : <T, U>((T, U), (T, U), (T, T) -> Order, (U, U) -> Order) -> Order =
func (p1, p2, cU, cT) {
   switch (cT(p1.0, p2.0)) {
     case (#equal) { cU(p1.1, p2.1) };
     case ord { ord };
   };
};

@kamil is that correct?