Update manual/contrib.texi

[Roland McGrath]

> I've reviewed the NEWS section for for 2.16 and propose to add the
> following entries to the manual.

I didn't try to vet the contents for wrong or missing additions,
but I don't see any obvious problems.

>  @item
> +Tulio Magno Quites Machado Filho for adding a new class of installed
> +headers for low-level platform-specific functionality.

...and one such for powerpc.

>  @item
> +Will Schmidt for optimized functions on PowerPC.

The other similar items mention what kinds of functions they are.
>From the ChangeLog it looks like all Will's additions are string functions.


Thanks,
Roland