libxml2: fix CVE-2014-3660

libxml2: fix CVE-2014-3660

It was discovered that the patch for CVE-2014-0191 for libxml2 is
incomplete.  It is still possible to have libxml2 incorrectly perform
entity substituton even when the application using libxml2 explicitly
disables the feature.  This can allow a remote denial-of-service attack on
systems with libxml2 prior to 2.9.2.

References:
    http://www.openwall.com/lists/oss-security/2014/10/17/7
    https://www.ncsc.nl/actueel/nieuwsberichten/kwetsbaarheid-ontdekt-in-libxml2.html

Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>