[Rivet] Can't succeed build Rivet-1.7.0 on intel Mac lion 10.7.3

[Hendrik Hoeth]

Thus spake Andy Buckley (andy.buckley at ed.ac.uk):

> I'm afraid that I can't work out from this what could be wrong...

Looks like yaml. I think it's fixed in r973 of our yaml-cpp, date
2012-02-03. So Rivet 1.8.0 should work.

-- 
Man is the best computer we can put aboard a spacecraft, and
the only one that can be mass produced with unskilled labor.
                                        -- Wernher von Braun