Flag mechanisms as SECURE; update digest-md5

Author: Ben Weaver

sasl/mechanism.py

@@ -10,9 +10,6 @@
 
 <http://tools.ietf.org/html/rfc2222>
 <http://www.iana.org/assignments/sasl-mechanisms>
-
-Copyright (c) 2009, Coptix, Inc.  All rights reserved.
-See the LICENSE file for license terms and warranty disclaimer.
 """
 from __future__ import absolute_import
 import abc, re
@@ -52,6 +49,8 @@ class Mechanism(object):
     __metaclass__ = MechanismType
     __slots__ = ()
 
+    SECURE = False
+
     @abc.abstractmethod
     def challenge(self):
         """Issue a challenge."""