Stop TypeTuple as template parameter from expanding

[Tobias Pankrath]

bearophile wrote:

> It's the design of typetuples, they are auto-flattening. I have never
> appreciated this design. Maybe Walter likes them this way, or they can't
> be designed in another way, I don't know.

I do like it, just it would be nice to have an alternative in phobos, iff 
there is no other way I am not aware of.