Updating top-level autoconf to 2.59

[Paolo Bonzini]

> Someone needs to decide which part of this to fix.  We can either fix
> make install in the gcc subdirectory to not do the bogus extra copy,
> or we can try to adjust things to install unprefixed in that case.
> 
> I prefer the former, i.e. install only i686-pc-linux-gnu-gcc.  This
> is a change, but it's also in line with autoconf's choices, and it's
> always much simpler to go along with autoconf than to fight it.

I'd prefer not changing what is installed, but if people agree to go the 
other way round I've no problem with that.

Anyway, we need to make sure that binutils/gas/ld do the same as gcc.

Paolo