maintain compatibility with older _notifyChange arguments.

Author: Steven Orvell

src/lib/bind/accessors.html

@@ -20,8 +20,9 @@
 
     _modelApi: {
 
-      _notifyChange: function(event, value) {
-        // use a cached event here (_useCache: true) for efficiency
+      _notifyChange: function(source, event, value) {
+        value = value === undefined ? this[source] : value;
+        event = event || Polymer.CaseMap.camelToDashCase(source) + '-changed';
         this.fire(event, {value: value}, 
           {bubbles: false, cancelable: false, _useCache: true});
       },

src/lib/bind/effects.html

@@ -41,7 +41,7 @@
 
     _notifyEffect: function(source, value, effect, old, fromAbove) {
       if (!fromAbove) {
-        this._notifyChange(effect.event, value);
+        this._notifyChange(source, effect.event, value);
       }
     },