One more forward port of CMSSW_7_2_X into CMSSW_7_3_X

Forward port of a few remaining PR from CMSSW_7_2_X to CMSSW_7_3_X.

In `Configuration/PyReleaseValidation/python/relval_steps.py` I dropped a comment:

    #### generator test section ####

which was in `CMSSW_7_2_X` but not in `CMSSW_7_3_X`.

In `Configuration/Generator/python/Pythia8CommonSettings_cfi.py` I kept:

     'ParticleDecays:tauIgnoreSpinUpCMSSW = on',

which was part of `CMSSW_7_3_X`, but not in `CMSSW_7_2_X`.

In `CommonTools/RecoAlgos/plugins/JetDeltaRTagInfoValueMapProducer.cc` I kept:

    if( matched_index>=0 && static_cast<size_t>(matched_index) < h_tagInfos->size() )

rather then the `CMSSW_7_2_X` version which had `unsigned`.