stock-config-files-handling      #6079
    o stock-config files handling on program load to preserve any
      user changes to config files (move to archive directory) and
      allow copy in of freshest version of shipped stock config files.
    o enhance stock-config menu to handle access to archive directories.
      - also extended to the 'radio/import from stock config' menu.

Additional note on stock configuration files:
  In order to prevent overwriting user-copy stock config files
  with shipped versions, CHIRP skips the copy of those files
  which already exist in the user-copy directory, leaving any
  new data in shipped versions in the shipped stock config directory.
  This function examines each pair (shipped vs user copy) and if
  different, moves the user-copy stock config to an archive directory,
  thereby permitting CHIRP to copy the newer shipped version to the
  user-copy directory. This new archive retains any user-modified data.