[Patch] First bits of the algo merge

[Paolo Carlini]

chris jefferson wrote:

>Ah, thats cool. I thought the problem was that doing this kind of thing
>at all would break things which worked before. Expanding it to work on
>even more things is of course fine :)
>  
>
Yes, it's nice!

>The only (tiny) thing that worries me is that I have come across code
>where people have defined their own iterator classes, and either
>incorrectly, or not at all defined iterator::value_type, and this is
>going to break their code. Of course we can just tell them to learn to
>write iterators correctly.
>  
>
About this, I did a quick grep and discovered that we are already
explicitely using value_type in quite a few places...

Paolo.