No ad-hoc polymorphism (overloading) for class methods

With normal methods:
```
options gen2

class Example {
    def foo(x : int; y : string) {}

    def foo(x : int) {
        foo(x, "123")
    }
}

[export]
def main() {
}

```

With abstract method:
```
options gen2

class Example {
    def abstract foo(x : int; y : string) : void

    def foo(x : int) {
        foo(x, "123")
    }
}

[export]
def main() {
}
```
