Make the pack command produce a predictable image file from the same content source.

[Aerocatia]

Currently, running the pack command using a image file as input will produce different image files on subsequent runs, although the image content hash produced with xdvdfs checksum always matches.

Using Halo as an example we get this:
If we have a raw dump that matches the redump databse as Halo - Combat Evolved (USA).iso
the image hash will be b8fda9630d1098cfcb46a59cab7e92031bede480661e7ee9f3a23f99dd711c74

Re-packing it with xdvdfs pack will shrink the image as expected, and you will get this:
Halo - Combat Evolved (USA).xiso.iso 50d6513db22cf50628c984637fcd9d6184b5ae37b5833f3249751cd155869024

However, if you run pack again using this file as input a different file will be produced.
Halo - Combat Evolved (USA).xiso.xiso.iso fc448a6f944161f6bb71a2b1a21b727c5836495973de83e034de11e9cdc8c28c

In all cases the content hash is 1f9e0b64febe43b397b0a9b2bec682f9dac9aac48c10530432141054742cbe7a

Ideally, running pack on an iso more that once will not produce a different file provided the same version of xdvdfs is used and the image generation logic has not changed.

This is useful because ideally we don't want the output file to change if the pack process ends up being run more than once for whatever reason unless something actually changed. (e.g. you might run a script to repack a directory of mixed images)

Comparing the images it seems things end up in a different order. I have not looked into it but perhaps this can be solved by sorting something somewhere?