AliAnaElectron (Jenn):

AliAnaElectron (Jenn):
Added Mark's btag QA histos
Added three event level QA histos:  impactXY, refmult and refmult2
Added Protection for AliAODPid pointer
Added "Misidentified" electron plots and renamed "Prompt" to "All"
Corrected the definition of xsi
Turned off cut on impactZ in GetBtag()
Set Btag bit in AliAODPWG4Particle according to number returned by GetBtag()

AliAODPWG4Particle(Jenn): Correct init value of Btag bit and add bit checking methods

Readers: Change the access to the vertex, make sure it is the best primary vertex
                Access the output AOD in case the merging of events was executed in the handler

AliAnaCalorimeterQA: Set some protections in case of MC data not available.