challenge #2: implement the vararg_reduce metafunction

[Andrei Alexandrescu (See Website For Email)]

My previous post defines max by availing itself of a metafunction called 
vararg_reduce. Your challenge is to define it. vararg_reduce takes an 
alias which it assumes is a function of two arguments, and it defines a 
vararg function that applies that alias repeatedly, similarly to the 
reduce primitive that is present in functional languages. Again, for 
background on functional reduce, see e.g.:

http://www.joelonsoftware.com/items/2006/08/01.html

Define vararg_reduce to deduce the result type properly, and to generate 
code as efficient as possible.


Andrei