TypeFunction example: reason about class hierachies

[Stefan Koch]

Hi Folks,

Luckily no one uses type functions yet otherwise I would have to 
announce a breaking change.
The type of types changed it's name again from __type to __type__.

Since it turns out that the glibc in.h header uses __type as a 
parameter name already.
Let's hope no one is using __type__.
Because the only option I have after that is 
'__type___make_______bloody_sure____no_one_____uses_this____as_an_identifier'

The code below should be fairly self explanatory.

Please let me know what you think

---
alias type = __type__;
type getSuper(type T)
{
     return __traits(getSuper, T);
}

class B {}
class C : B{}
class D : B {}
bool eq(type A, type B)
{
     return is(A == B);
}

pragma(msg, getSuper(B).eq(getSuper(C)) ); // false
pragma(msg, getSuper(C).eq(B) ); // true
pragma(msg, getSuper(D).eq(getSuper(C)) ); // true
---

P.S. getting is(Myclass SuperType == super) to work, requires 
unreasonably much code.
Since I would need to extend my partial evaluation system ... 
let's not go into it.
I can explain it though if desired.
Besides ... the syntax is one of the things I always look up.
__traits(getSuper) should be more intuitive.