I want to add a Phobos module with template mixins for common idioms.

[Idan Arye]

At any rate, I am forced to admit I made a mistake about 
`hasIntance()` not needing synchronization. I neglected the 
possibility that the constructor(or anything else used for 
initialization) can throw!

The compiler might decide that it's better to write the global 
reference first, and if the initializer throws just set it back 
to null. If that is the case, `hasInstance()` could see that the 
global reference is not null and return true, and then the 
initializer will throw and the initializing thread will set the 
global reference to null again.

So yea, I'm gonna have to synchronize it too...