TChain tests successful

All TChain tests are now successful most of the time. There is still some undeterministic behaviour to be tracked down, but it does not happen very often, which makes it hard to track (might be fixed now). There is an overhaul to the way leaves are read to support the TChain. I am also manually detecting when the TTree changes in the TTreeReaderValueBase to make sure the local Leaf pointer is correct.