Object.toString, toHash, opCmp, opEquals

[Walter Bright]

Perhaps I can help things work for you and Timon:

```
import std.stdio;

class A
{
     string xxx(const Object) const { return "A"; }
}

class B : A
{
     alias xxx = A.xxx;
     string xxx(Object) { return "B"; }
}

void main()
{
     const A a = new A();
     B b = new B();
     const B c = new B();
     writeln(a.xxx(a));
     writeln(b.xxx(b));
     writeln(c.xxx(c));
}
```
I'm calling this xxx instead of toString, just so I can show all the code. 
Compiling it and running it prints:

A
B
A

In other words, you can have a toString() that is mutable and it will work fine 
with writeln(), because writeln(x) does not look for Object.toString(), it looks 
for x.toString().

Does this work for you?