libio patches for glibc 2.1

[Joe Buck]

> > Ah, so the disruption is just for extended and wide streams?  Then it
> > seems that it should be a one-time thing.
> 
> Not if I missed something.  Wide streams are still not supported since
> I've yet to decide how to implement this correctly.  But I've added
> some unused padding bytes at the end of the struct so that we can add
> new members later.

Since on the C++ side the wide streams are a different template expansion,
it seems that you are free to use a completely new struct for the libio/C
side of wide streams.