Q# namespaces with the same fully-qualified name as a callable or type produce invalid C# code

This program is accepted by the Q# compiler:

```
namespace Foo {
    function Bar() : Unit { }
}

namespace Foo.Bar {
    function Hello() : Unit { }
}
```

But it produces this C# compile error:

> obj\qsharp\src\Program.g.cs(26,26): error CS0101: The namespace "Foo" already contains a definition for "Bar".