Update zsync to 0.4.1.
From the maintainter's webpage (http://zsync.moria.org.uk/):
This is just a bugfix release. Someone noticed that zsync would be vulnerable to CAN-2005-2096, due to it's use of zlib code. So the patch for that is now done. This release also includes some HTTP protocol fixes, as there have been some complaints/observations on how zsync failed to correctly implement some details from the standard.