leftover after clean

[Dirk Hohndel]

On Wed, Aug 20, 2014 at 11:32:03PM +0200, Salvo Tomaselli wrote:
> > the file
> > ssrf-version.h
> > which is not in the original tarball, remains around after a make clean.
> 
> Just noticed that also "subsurface" and "Makefile" are in the same situation

I don't think we'd want to delete Makefile - but maybe that's something
that others feel differently about.

At least for me ssrf-version.h is already being deleted.
I'll make sure the TARGET is added to be deleted by make clean as well

/D