fail2ban - security update

• Use anchored failregex for filters to avoid possible DoS. Manually
  picked up from the current status of 0.8 branch (as of
  0.8.13-29-g09b2016):
  • CVE-2013-7176: postfix.conf - anchored on the front, expects
    “postfix/smtpd” prefix in the log line
  • CVE-2013-7177: cyrus-imap.conf - anchored on the front, and
    refactored to have a single failregex
  • couriersmtp.conf - anchored on both sides
  • exim.conf - front-anchored versions picked up from exim.conf
    and exim-spam.conf
  • lighttpd-fastcgi.conf - front-anchored picked up from suhosin.conf
    (copied from the Wheezy version)
• Catch also failed logins via secured (imaps/pop3s) for cyrus-imap.
  Regression was introduced while strengthening failregex in 0.8.11 (bd175f)
  Debian bug #755173
• cyrus-imap: catch user not found attempts

For Debian 6 Squeeze, these issues have been fixed in fail2ban version 0.8.4-3+squeeze3