USN-5638-4: Expat vulnerabilities

USN-5638-1 fixed several vulnerabilities in Expat. This update provides
the corresponding update for Ubuntu 14.04 ESM.

Original advisory details:

Rhodri James discovered that Expat incorrectly handled memory when
processing certain malformed XML files. An attacker could possibly
use this issue to cause a crash or execute arbitrary code.

advisory code crash expat files issue james malformed memory ubuntu update usn vulnerabilities xml