Proper currying

Adapt the dynamic builtins to support proper currying. Make sure this doesn't break anything else that is more widely a standard.

E.g.:

```prolog
?- C = goal(Var1), apply(C, [Var2]). % is equivalent to goal(Var1, Var2)
```

and 
```prolog
?- curry(goal, [Var1], Curried).
Curried = goal(Var1).
?- curry(goal(Var1), [Var2], Curried).
Curried = goal(Var1, Var2).
```