Use SASL DIGEST-MD5 authentication over unsecured network connections only.

This authentication mechanism is implemented under the iksemel API, which
makes use of GnuTLS, whereas we use OpenSSL. Note : there's ongoing
dicsussion at the SASL IETF WG in order to deprecate SASL DIGEST-MD5, see
http://ietfreport.isoc.org/ids-wg-sasl.html.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@96499 65c4cc65-6c06-0410-ace0-fbb531ad65f3