squid: Update to 3.4.8

Contains some security fixes:

 * CVE-2014-6270
   http://www.squid-cache.org/Advisories/SQUID-2014_3.txt
 * CVE-2014-7141
   CVE-2014-7142
   http://www.squid-cache.org/Advisories/SQUID-2014_4.txt