change event is fired when the checked state changes due to user

interaction. Use `core-change` event for old behavior (fired when the
checked state changes).

Fixes #9

paper-checkbox.html

@@ -75,10 +75,16 @@
   Polymer('paper-checkbox', {
 
     /**
-     * Fired when the checked state changes.
+     * Fired when the checked state changes due to user interaction.
      *
      * @event change
      */
+
+    /**
+     * Fired when the checked state changes.
+     *
+     * @event core-change
+     */
 
     toggles: true,
 
@@ -89,7 +95,7 @@
       cl.toggle('checkmark', !this.checked);
       cl.toggle('box', this.checked);
       this.setAttribute('aria-checked', this.checked ? 'true': 'false');
-      this.fire('change');
+      this.fire('core-change');
     },
 
     checkboxAnimationEnd: function() {