fix for correct handling of pathological cases of Pt=0 groomed jets
now discarding matches where two jets are too far apart
Merge pull request #3997 from cms-btv-pog/JetFlavourClusteringFix_from-CMSSW_6_2_X_SLHC_2014-05-23-1400

Fix for jet flavour clustering: Backport from 7_1_X to 6_2_X_SLHC