Fix a potential crash issue discovered by Alexander Cherepanov:
It seems bsdtar automatically handles stacked compression. This is a
nice feature but it could be problematic when it's completely
unlimited. Most clearly it's illustrated with quines:
$ curl -sRO http://www.maximumcompression.com/selfgz.gz
$ (ulimit -v
10000000 && bsdtar -tvf selfgz.gz)
bsdtar: Error opening archive: Can't allocate data for gzip decompression
Without ulimit, bsdtar will eat all available memory. This could also
be a problem for other applications using libarchive.