make statics class members
change static int -> static std::atomic<int>
change static int -> static std::atomic<int>
use std::atomic<bool>::compare_exchange_strong() to ensure messages only appears once
Merge pull request #1430 from gartung/statics-RecoMET-METAlgorithms

Multithreading fixes -- Make statics class members in RecoMET/METAlgorithms