add copyMVA parameter in order to handle also track collections not associated to any MVA value map (i.e., some track collection used @HLT)
Merge pull request #6605 from mtosi/from-CMSSW_7_3_X_2014-11-21-0200_fixTrackListMerger

Add copyMVA parameter in MultiTrackMerger (forward port of #6535)