Tag object initialization not guaranteed legal

[Dave Abrahams]

We should be using this technique: ​http://tinyurl.com/threadsafe-static-globals

[Daniel Wallin]

Isn't that exactly what we are already doing?

template <class tag>
struct keyword
{
    ...
    static keyword<Tag> const instance;
};

template <class Tag>
keyword<Tag> const keyword<Tag>::instance = {};

...

    namespace                                                       \
    {                                                               \
       ::boost::parameter::keyword<tag_namespace::name> const& name \
       = ::boost::parameter::keyword<tag_namespace::name>::instance;\
    }