Keep ROOT from optimizing Streamers

ROOT will optimize Streamers such that adjoining member data of the same basic type are written/read
together. Sometimes ROOT decides this optimization should not be applied and de-optimizes the Streamer.
Unfortunately, the decision to de-optimize comes very late and can happen during the event loop and cause
a data race. Therefore we tell ROOT, for now, to never optimize.
Merge pull request #2391 from Dr15Jones/keepRootFromOptimizingBranches

Keep ROOT from optimizing Streamers