message: fix a flag and eventheader for generator to make it work for onthefly
diff: #include <AliAODMCParticle.h>
  #include <AliMCEvent.h>
  #include <AliGenHijingEventHeader.h>
  +#include <AliGenDPMjetEventHeader.h>
  #include <AliAnalysisManager.h>
  #include <AliAnalysisDataContainer.h>
  #include <AliAODEvent.h>
  @@ -162,7 +163,7 @@ void AliJCatalystTask::UserExec(Option_t* /*option*/)
  fInputList->Clear();
  fInputListALICE->Clear();
  - float fImpactParameter = -1.0f;
  + float fImpactParameter = .0; // setting 0 for the generator which doesn't have this info.
  double fvertex[3];
  fEvtNum++;
  @@ -172,7 +173,7 @@ void AliJCatalystTask::UserExec(Option_t* /*option*/)
  // load current event and save track, event info
  if(flags & FLUC_KINEONLY) {
  AliMCEvent *mcEvent;
  - if(FLUC_KINEONLYEXT) {
  + if(flags & FLUC_KINEONLYEXT) {
  AliInputEventHandler* fMcHandler = dynamic_cast<AliInputEventHandler*> (AliAnalysisManager::GetAnalysisManager()->GetMCtruthEventHandler());
  mcEvent = fMcHandler->MCEvent();
  @@ -185,12 +186,12 @@ void AliJCatalystTask::UserExec(Option_t* /*option*/)
  }
  if(!fnoCentBin) {
  - AliGenHijingEventHeader* headerH = dynamic_cast<AliGenHijingEventHeader*>(mcEvent->GenEventHeader());
  - if(!headerH)
  - return;
  - //Double_t gReactionPlane = headerH->ReactionPlaneAngle();
  - Double_t gImpactParameter = headerH->ImpactParameter();
  - fcent = GetCentralityFromImpactPar(gImpactParameter);
  + AliGenHijingEventHeader* hijingHeader = dynamic_cast<AliGenHijingEventHeader*>(mcEvent->GenEventHeader());
  + AliGenDPMjetEventHeader* dpmHeader = dynamic_cast<AliGenDPMjetEventHeader*>(mcEvent->GenEventHeader());
  + if (hijingHeader) fImpactParameter = hijingHeader->ImpactParameter();
  + else if (dpmHeader) fImpactParameter = dpmHeader->ImpactParameter();
  +
  + fcent = GetCentralityFromImpactPar(fImpactParameter);
  }
  if(flags & FLUC_ALICE_IPINFO){
  //force to use ALICE impact parameter setting
  