gzip shouldn't raise ValueError on corrupt files
Currently the gzip module will raise a ValueError if the file was
corrupt (bad crc or bad size). I can't see how that applies to
reading a corrupt file. IOError seems better, and it's what code
will likely be looking for.
The last round boosted "the limit" from 2GB to 4GB. This round gets
rid of the 4GB limit. For files > 4GB, gzip stores just the last 32
bits of the file size, and now we play along with that too. Tested
by hand (on a 6+GB file) on Win2K.
Boosting from 2GB to 4GB was arguably enough "a bugfix". Going beyond
that smells more like "new feature" to me.
Fixed the signed/unsigned confusions when dealing with files >= 2GB.
4GB is still a hard limitation of the gzip file format, though.
Testing this was a bitch on Win98SE due to frequent system freezes. It
didn't freeze while running gzip, it kept freezing while trying to *create*
a > 2GB test file! This wasn't Python's doing. I don't know of a
reasonable way to test this functionality in regrtest.py, so I'm not
checking in a test case (a test case would necessarily require creating
a 2GB+ file first, using gzip to zip it, using gzip to unzip it again,
and then compare before-and-after; so >4GB free space would be required,
and a loooong time; I did all this "by hand" once).
Bugfix candidate, I guess.
