RF remove redundant code

- rotate_all does not add enough
- not safe to add more to it, like auto-delete
TEST: refactor
ENH: rotate secure-deletes original if rotation succeeded

- delete orig.enc should not be done by default, to avoid data loss
- should be able to be done easily, because orig.enc is suspect (= the reason to rotate)
- solution: original enc file is wipe()d if can verify the rotation:
  1) explicitly given priv_new (to decrypt the just-encrypted file)
  2) AND the unencrypted file contents match (ignoring padding differences)
RF: rename wipe -> destroy; randomly overwrite padding info in unpad