Add <initializer_list> to stdc++.h and ruminations on aggregation headers

[Benjamin Kosnik]

> I was looking at Bjarne Stroustrups proposal n2905.pdf for
> aggregation headers and looking at our own in precomp.

Yeah.
 
> His std-all is basically our stdc++.h except that the latter doesn't 
> have <initializer_list>.  I know it really is in there but I thought
> it might be nice to put it in there explicitly for forms sake.  See
> the patch and changelog.

This is ok, please check it in.
 
> Also attached are simple implementations of std-all and std-checked
> to play with and some toy drivers.

If/when something like this goes in, would rather rename stdc++.h to
whatever is standardized, and then build on it with std-checked just
defining _GLIBCXX_DEBUG and including stdc++.h. h

> We could add an ext-all.

That is what extc++ should be. If things are missing add them please.

> Of course these aggregation headers are not in the std yet ;-).
> These are just to think about.

Of course.

My own feeling is that the single header, stl.h or stdc++.h or however
it is spelled, is useful and makes sense to standardize. (If only to to
provide an abstract interface to precompiled headers as is the
libstdc++ usage.)

I don't really see much use for other ones. 

-benjamin