Bug in module gzip

[Jeremy Hylton]

I would guess that you're using the new gzip.py but not the new zlib
module.  The unused_data attribute was added to fix a bug in gzip.py,
which prevented it from properly handling gzip-created files that
contained multiple, independent compressed chunks.  (Did I say that at 
all clearly?)

with the gzip utility you can do the following:
cat part1.txt >> input
cat part2.txt >> input
gzip part1.txt
gzip part2.txt
cat part2.txt.gz >> part1.txt.gz
gzip -d --stdout part1.txt.gz > output
diff input output
[reports no difference]

Getting this right involved changing the interface to zlib.

Jeremy