fileutils.AtomicSaver: merge dest_perms and part_perms into one more intuitive, more secure file_perms argument. Update AtomicSaver docs accordingly.
fileutils.AtomicSaver: merge dest_perms and part_perms into one more intuitive, more secure file_perms argument. Update AtomicSaver docs accordingly.

zeroSteiner/boltons,markrwilliams/boltons,doublereedkurt/boltons,suranap/boltons