DSA-3744 libxml2 - security update

Several vulnerabilities were discovered in libxml2, a library providing
support to read, modify and write XML and HTML files. A remote attacker
could provide a specially crafted XML or HTML file that, when processed
by an application using libxml2, would cause a denial-of-service against
the application, or potentially, the execution of arbitrary code with
the privileges of the user running the application.