USN-4899-2: SpamAssassin vulnerability

USN-4899-1 fixed a vulnerability in SpamAssassin. This update provides the corresponding update for Ubuntu 14.04 ESM. Original advisory details: Damian Lukowski discovered that SpamAssassin incorrectly handled certain CF files. If a user or automated system were tricked into using a specially- crafted CF file, a remote attacker could possibly run arbitrary code.