When using load_particles to load simulation particles from a file, in the past the particles
had to enter through one of the three planes z = zmin, z = zmax, or r = rmax. If a metal
boundary existed just inside the plane, particles would simply be eliminated. It is now possible
for particles to enter through the metal boundary on the left-hand side of the simulation
region. This feature was added following a request from J. Edelen (FNAL).
The beam snapshot (from define_snapshots) now includes a status column that indicates
whether particles are active.