small improvement for fill and fill_n

[Paolo Carlini]

Nathan Myers wrote:

>Worse, I don't know if the extra copy is always allowed.  Anyway it's 
>easy to imagine a type for which it is would be too expensive to make 
>extra copies.  What we need is a way to assert explicitly that &value 
>doesn't alias anything else.  Failing that, we need a way to tell if
>copying is cheap and the value can be held in a register, so we can
>overload on that condition.  I think there's some work on that last
>for C++0x.
>  
>
Ah, ah! Indeed, I suspected that the cost of the copy had to be taken into
account, somehow...

Thanks, I'll try lo learn more about those issues,
Paolo.