[Patch] First bits of the algo merge

[Gabriel Dos Reis]

Paolo Carlini <pcarlini@suse.de> writes:

| >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...

Indeed.  I suspect the question would be whether we do it consistently and
systematically...

-- Gaby