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 #3996 from cms-btv-pog/JetFlavourClusteringFix_from-CMSSW_7_0_X_2014-05-23-1400

Fix for jet flavour clustering: Backport from 7_1_X to 7_0_X