util.sasl, util.sasl_cyrus: Use method:mechanisms() in method:select(), instead of using the mechanisms list directly (fixes a traceback).

util/sasl.lua

@@ -111,7 +111,7 @@ function method:select(mechanism)
 		return false;
 	end
 	
-	self.mech_i = self.mechs[mechanism];
+	self.mech_i = mechanisms[self.mechanisms()[mechanism] and mechanism];
 	return (self.mech_i ~= nil);
 end
 

util/sasl_cyrus.lua

@@ -144,8 +144,7 @@ end
 -- select a mechanism to use
 function method:select(mechanism)
 	self.mechanism = mechanism;
-	if not self.mechs then self:mechanisms(); end
-	return self.mechs[mechanism];
+	return self.mechanisms()[mechanism];
 end
 
 -- feed new messages to process into the library