Merged requested to merge jchapman/athena:WhiteListHepMC3Fix_master into master
It was noticed that quasi-stable particle simulation output differed between HepMC2 and HepMC3 builds.
The largest difference was due to the lack of a minimum decay radius cut for a particle to be considered as quasi-stable in HepMC3 builds. This merge request fixes this.
NB the code change is within an
#ifdef HEPMC3 block, so it will have no effect on the CI output, but has been tested locally.
After this, some particle ordering differences persist, but it is not clear whether these can be removed. This will be dealt with in a separate merge request if possible.