Cyclic default-bindings in functions are still accepted

[Martin Sjölund]

The check should probably be moved to the instantiation of functions (because we fall back to generation of code). We can check for usage of unbound variables in the same place later on...

{{{function f

output Real y = y;

end f;

class A

Real y = 5.79776549334303e-316;

end A;
Error: Cyclically dependent constants or parameters found in scope : {y}
}}}