'Reset state variables used for each pass.'

def _reset_state(self):

    self.used_images = {}
    self.instance_names = set()
    self.back_swap_images = set()
    self.used_swap_images = set()
    self.active_base_files = []
    self.originals = []
    self.removable_base_files = []
    self.unexplained_images = []
