TMVA: Prevent stack corruption for user supplied trees.

We will be reading the tree, so make sure that the user
did not forget to remove pointers to out-of-scope vars.

The user should *always* call ResetBranchAddresses on their trees
when they are done with them, but in case they forgot this can save
some debugging time at no cost.

tmva/tmva/src/DataSetFactory.cxx

@@ -288,6 +288,7 @@ void TMVA::DataSetFactory::ChangeToNewTree( TreeInfo& tinfo, const DataSetInfo &
    TTree *tr = tinfo.GetTree()->GetTree();
 
    tr->SetBranchStatus("*",1);
+   tr->ResetBranchAddresses();
 
    Bool_t hasDollar = kFALSE;