small improvement for fill and fill_n

[Paolo Carlini]

Hi Martin,

> IMO, this sounds more like a library issue than a simple matter of
> QoI. It's easily detectable whether the algorithm actually "Assigns
> value through all the iterators..." as the standard specifies or not.
> There are places in the library where the interface goes to extra
> trouble (of using by-value arguments) to avoid this side-effect of
> aliasing.

Thanks for your message: please confirm that I understand well your
point. You mean that the library (i.e., the Standard) should be perhaps
improved in this area to more carefully select a type of argument
passing (e.g., by value) that automatically avoids this kind of trouble?

Paolo.