- it is not necessary to compute the digest when adding files -- saves time

- it is not necessary to compute the digest when adding files -- saves time
- checkin: update local copy in store (fixes diff using obsolete old version)
- use shutil.copy2 instead of home-grown copy_file
- make put_source_file() and delete_source_file() methods of the Package class;
  rename delfile method to delete_localfile