fixed the contents of RecoBTag/PerformanceDB/python/measure/Pool_btagMistagWinter13.py
Merge pull request #3164 from cms-btv-pog/RecoBTagPerformanceDB-Bugfix_from-CMSSW_7_1_0_pre5

RecoBTag/PerformanceDB -- Fixed the contents of RecoBTag/PerformanceDB/python/measure/Pool_btagMistagWinter13.py