Merge branch 'la/trailer-cleanups'

Code clean-up. Keep only the first three clean-ups, and discard the rest to be replaced later. cf. <owly1qetjqo1.fsf@fine.c.googlers.com> cf. <owlyzg1dsswr.fsf@fine.c.googlers.com> * la/trailer-cleanups: trailer: split process_command_line_args into separate functions trailer: split process_input_file into separate pieces trailer: separate public from internal portion of trailer_iterator