Hepmc3 nightly fixes 09122020 part 2

Andrii Verbytskyirequested to merge
averbyts/athena:hepmc3_nightly_fixes_09122020_part_2 into master

In this MR:

  • Use C++11 loops to assure HepMC3 compatibility.
  • Use free function HepMC::signal_process_id()
Edited by Andrii Verbytskyi

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