samba: update to 3.6.20.

These are security releases in order to address CVE-2013-4475
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-4475
(ACLs are not checked on opening an alternate data stream on
a file or directory) and CVE-2013-4476
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-4476
(Private key in key.pem world readable).