replaced runtime cms::Exception calls with edm::LogError calls
added default ghost rescaling factor
replacing repeating code blocks with function calls
Merge pull request #3785 from cms-btv-pog/JetFlavourLogError_from-CMSSW_7_1_X_2014-05-09-1400

AT -- Replacing runtime cms::Exception calls with edm::LogError calls in the jet flavour code