Code review comment for lp:~sbeattie/ubuntu/karmic/zsync/zsync-fixups

In the last sync, from and to were reverted from off_t (64bit types) to ints, which suffers from signed overflow when the partially downloaded file is larger than 2GB. This fix reverts most of the merge's change for this section, while keeping the intent, which is to take global_offset into account when computing rf->offset. I've tested this fix and it causes zsync to successfully download daily dvds where the 0.6-1ubuntu1 would consistently SEGV. It would be nice if this could be merged for alpha 5, since iso testers for that release may want to use zsync to grab the images for testing.