updated to combine files that may have different number of LHE processes or parton shower cross sections
fix the average for cross section after filter
Merge pull request #6624 from syuvivida/73X_xsec_new

Updated GenXSecAnalyzer and GenLumiInfoProduct for combining files correctly
Merge remote branch 'origin/CMSSW_7_4_X' into CMSSW_7_0_X