A new PR (this is the same as PR#5954 and meant to replace that...).
(ref: PR#5954 https://github.com/cms-sw/cmssw/pull/5954)
Cannot merge...
Fix the negative indices issue
Switch from "customize method 2" to customize method 1.
Fix the HcalSeverityLevelComputer.cc to the correct one
Merge pull request #6150 from lihux25/threadsafe_faster_hcal25ns_RECO_method2

Replacing PR#5954: Threadsafe faster hcal25ns reco method2