task/us68-ta82 -- Create a simple throwaway method to re-archive
existing FTP files

nparcel/ftp.py
* updated the archive_branch() method signature to include the "ymd"
  attribute so override the timestamp token from current time if
  supplied
* new method migrate_archived_files() identify old-style archived files
  and migrate to the new archiving arrangement

nparcel/utils/files.py
* patch bug in the move_file() function as it was ignoring the "err"
  parameter and unconditionally moving aside file that failed the move