[gfortran patch] use libtool version info

[Matthias Klose]

Steven Bosscher writes:
> > Is there a reason to start with 6 as the version number? Or should the
> > be 1?
> 
> We probably copied it over from libstdc++  ;-)
> 
> I think we should start at version 1, or even 0.x.y until the library
> is finished.  Thoughts, others?

I checked it in with 0, such that the soname doesn't change (compared
to HEAD before this patch).

	Matthias