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
diff --git a/lib/zip.h b/lib/zip.h
index 014df7a..48431a3 100644
--- a/lib/zip.h
+++ b/lib/zip.h
@@ -65,6 +65,7 @@
 #define ZIP_FL_NODIR		2 /* ignore directory component */
 #define ZIP_FL_COMPRESSED	4 /* read compressed data */
 #define ZIP_FL_UNCHANGED	8 /* use original data, ignoring changes */
+#define ZIP_FL_RECOMPRESS      16 /* force recompression of data */
 
 /* archive global flags flags */