[Rivet] rivet 2 on Mac OSX

[Frank Siegert]

> Since there are no other fixes so far, no-one else has hit this issue,
> and it doesn't change the behaviour of a successful build, I am tempted
> to just "silently" remake the Rivet and YODA tarballs with this fix
> included. A bit naughty, but it's not worth a full release and ~everyone
> except Hannes will not notice at all! A more proper way is to make e.g.
> Rivet-2.1.2.post1, cf. Python's version scheme
> http://legacy.python.org/dev/peps/pep-0440/#post-releases ... but I find
> it a bit ugly and confusing. Preferences, developers?

Silently replacing is fine with me, but please do let us know once you
have done so, then I'll update the md5sums e.g. in the Arch
PKGBUILD's.

Cheers,
Frank