Backport for Validation/EventGenerator from CMSSW_7_3_X_2014-11-17-0200 ...

...to 7_2_X. Includes upgrade to TauValidation(ie genparticle collection to allow same code to be run at reco and genvalid) and minor fixes. 11/17/2014 (nugent@physic.rwth-aachen.de)