mixin template silently `override` without even a warning message!

[mw]

Even more fun when we have attribute of the same name:

```
import std;

template Foo() {
     int a;
     void foo() {writeln(a);}
     void bar() {foo();}
}

class A {
     mixin Foo;
     int a;
     void foo() {writeln(a);}
}

void main() {
     A a = new A();
     a.a = 911;
     a.bar();  // print 0
     a.foo();  // print 911
}
```

So `class A` has another hidden `Foo.a` attribute, but cannot 
read / write it's value outside of Foo?