libidn - security update

Hanno Boeck discovered multiple vulnerabilities in libidn, the GNU
library for Internationalized Domain Names (IDNs), allowing a remote
attacker to cause a denial of service against an application using the
libidn library (application crash).

For the stable distribution (jessie), these problems have been fixed in
version 1.29-1+deb8u2.

For the testing distribution (stretch), these problems have been fixed
in version 1.33-1.

For the unstable distribution (sid), these problems have been fixed in
version 1.33-1.

We recommend that you upgrade your libidn packages.