[Rivet] yaml-cpp upgrades for Rivet 2 and LHAPDF 6

[Andy Buckley]

Hi all,

Some of you probably noticed today via SVN commit messages that I
updated both the Rivet 2.0.0 trunk and the LHAPDF6 branch to use the
interface of the newer 0.5.x series of yaml-cpp rather than the defunct
0.3.x that we were previously stuck on. As far as I can tell it's all
working fine. But if you build these from SVN now (or the next
releases), you will need to install a newer version of yaml-cpp.

I'm going to try to tick off some more TODOs in both packages in the
next couple of weeks, most notably the remaining "YODA TODOs" in Rivet
and the promised interface enhancements in LHAPDF. If you can help out
as well -- even small contributions would be much appreciated -- then
please do (and let me know so we don't end up with clashing commits or
duplicated effort).

Andy

-- 
Dr Andy Buckley, Royal Society University Research Fellow
Particle Physics Expt Group, University of Edinburgh