Message4901

Java's zip implementation doesn't support any partial flush modes like 
Z_SYNC_FLUSH (http://bugs.sun.com/bugdatabase/view_bug.do?
bug_id=4206909, http://bugs.sun.com/bugdatabase/view_bug.do?
bug_id=4255743), so we've disabled these modes and their associated 
flags. That way libs fail fast when trying to use it

However we should probably provide the flags for compatibility sake 
anyway. ntlk doesn't even seem to rely on this flush mode, it just 
references it because it subclasses gzip.GzipFile.flush which references 
it (as it's the default mode).

Our own GzipFile has a workaround for the lack of zlib.Z_SYNC_FLUSH, so 
supporting it would also rid us of that