POG reference implementation in, though data/mc corrections not yet applied
BaseJet: clarify that partonFlavour() is from showering, and add a method for the parton from hard scattering
QuarkGluonTagger: make the std::ifstream local, it doesn't need to be a datamember and gcc doesn't like it
QuarkGluonTagger: Implement Data/MC corrections from POG
Merge pull request #27 from gpetruc/QuarkGluonLikelihood-CMG_PAT_V5_18_from-CMSSW_5_3_14

Quark gluon likelihood