Btag cond format

This is the implementation of the new b-tag conditions format, as presented in the last talk of the AlCaDB meeting on 2014 Nov 10: https://indico.cern.ch/event/350636/
see my comment about removing cerr above. 
The exception handling in cmssw is explained in: https://twiki.cern.ch/twiki/bin/view/CMSPublic/SWGuideEdmExceptionUse