php-horde-core - security update

It was discovered that php-horde-core, a set of classes providing the
core functionality of the Horde Application Framework, is prone to a
cross-site scripting vulnerability.

For the stable distribution (jessie), this problem has been fixed in
version 2.15.0+debian0-1+deb8u1.

For the testing distribution (stretch), this problem has been fixed
in version 2.22.4+debian0-1.

For the unstable distribution (sid), this problem has been fixed in
version 2.22.4+debian0-1.

We recommend that you upgrade your php-horde-core packages.