Torrentzip is a program that brings zip archives into a ``normal
form'': if the contained files (and their names) are identical, the
zip archive will always be the same, byte-wise.  Below is the
definition fo the Torrentzip normal form.

* order of files in archive

  In ascending order, as determined by strcasecmp(3).

  XXX: How does it deal with file names differing in case only?


* compression used

  Deflate at best compression level:

  deflateInit2(..., Z_BEST_COMPRESSION, Z_DEFLATED,
  		    -MAX_WBITS, 8, Z_DEFAULT_STRATEGY);

* fields in local/central directory

  version made by		0
  version needed to extract	20
  general purpose flag		2 (maximum compression)
  compression method		8 (Deflated)
  last mod file time		0xbc00 (23:32 GMT+1)
  last mod file date		0x2198 (1996/12/24)
  extra fields			none
  file comment			none
  disk number start		0
  internal file attributes	0
  external file attributes	0

* archive comment:

  The archive comment contains a signature and a crc32 checksum of the
central directory (as specified by size/offset in EOCD record).  This
is used to detect wether a torrentziped archive was modified by a
non-torrentzip aware program.

  TORRENTZIPPED-XXXXXXXX where XXXXXXX is the crc32 checksum of
central dir in hex, using uppercase letters A-F.