Implement a class with mixins

[Frank Benoit]

I missed the Bar mixin in the previous posting.

> .class C{
> .  mixin Foo foo;
.  mixin Bar bar;
> .  public this(){
> .    foo.this( 2 ); // if missing => compile error
> .    // bar.this() is implicit called, manually call is possible
> .  }
> .}