TorrentZip support.

- two new functions (zip_get_archive_flag, zip_set_archive_flag)
  to manipulate archive-global flags, currently only wether an archive
  is/should be torrentzipped.
- new flag to zip_source_zip (ZIP_FL_RECOMPRESS) to force recompression
- new program to torrentzip existing archive.

--HG--
branch : HEAD