Small code review

[mist]

Subj: http://dpaste.dzfl.pl/dfab7219

I wanted to code a small extension to phobos typetuple module to 
extend basic available operations on type tuples more on par with 
std.algorithm ones. I don't have enough practice in 
metaprogramming "D way" though and would gladly listen any 
recommendations in both improving code style and possible ways to 
implement similar things in shorter and more canonical way.

Thanks!