Add setting for configuring output of PGUN simulation (@adavis)
See merge request !2393 (merged) (cherry picked from commit 076be4a8)
Needed to propagate pGun PV from Gauss through the Brunel processing step for 2015 pGun productions with Gauss v54r0 (Sim10) and Gauss v49r16 (Sim09) or later. To be activated for steps that process pGun, by setting SimConf().pGun=True