Added checkpoint_kill, written by JD, which dumps xvres files 1h before the end of wall clock (48h by default). This needed a new restart name in cubepm.par, a new elseif statement in particle_initialization.f90, and new segments in cubepm_kill.f90 (which replaces cubepm.f90 if that option is desired). Also, initial projection is no longer called by default.