Make example in 7.1.6.4 more meaningful.

In section __7.1.6.4 `auto` specifier__:

```cpp
namespace N {
  template<typename T> struct Wrap;
  template<typename T> Wrap make_wrap(T);
}
/* ... */
auto::Wrap<int> x = N::make_wrap(0); // error: auto used in a non-deduced context
```

This error case would be more meaningful if `N` is a `struct`, since `auto` cannot be a placeholder for a `namespace`.