Allow customization of indent inside namespace { ... }

QtCreator want's to indent all the content inside namespace XXX

:

namespace {
    class X {
    };
}

This leads to excessive indenting, especially if you have nested namespaces. Inside QtCreator, we (almost) never indent the content of a namespace. A quick google search for "indentation namespace coding style" also indicates that a lot of coding styles (e.g. for webkit) also advise to not indent the content of a namespace.