xorg-server, xorg-server-lts-trusty vulnerabilities

USN-2436-1 fixed vulnerabilities in the X.Org X server. Since publication,
additional fixes have been made available for these issues. This update
adds the additional fixes.

Original advisory details:

Ilja van Sprundel discovered a multitude of security issues in the X.Org X
server. An attacker able to connect to an X server, either locally or
remotely, could use these issues to cause the X server to crash or execute
arbitrary code resulting in possible privilege escalation.