add in protection to stabilize the behavior of PFClusterAlgo in large topo clusters
normalize cluster energy to rechit threshold when calculating fraction
protection against bad behavior in case of zero threshold
Adjust the shower sigma to 0.3 cm to cover the neighbouring strip.
Change in energy spectrum is expected.
Merge pull request #2490 from lgray/pfclusteralgo_stability

Reco updates -- Protection to stabilize the behavior of PFClusterAlgo