add 'map' reference to standard popup. make sure to nullify it in the destroy()

git-svn-id: http://svn.openlayers.org/trunk/openlayers@336 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Popup.js

@@ -37,6 +37,9 @@ OpenLayers.Popup.prototype = {
     /** @type String */
     border: "",
 
+    /** this gets set in Map.js when the popup is added to the map
+     * @type OpenLayers.Map */
+    map: null,
 
     /** 
     * @constructor
@@ -66,6 +69,7 @@ OpenLayers.Popup.prototype = {
             this.div.parentNode.removeChild(this.div);
         }
         this.div = null;
+        this.map = null;
     },
 
     /**