applying (yet another) patch for #549. this one eliminates the double-destruction of the map due to the unload of window

git-svn-id: http://svn.openlayers.org/trunk/openlayers@2874 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -33,6 +33,12 @@ OpenLayers.Map.prototype = {
     /** @type OpenLayers.Events */
     events: null,
 
+    /** function that is called to destroy the map on page unload. stored
+     *   here so that if map is manually destroyed, we can unregister this.
+     * 
+     * @type Function */
+    unloadDestroy: null,
+
     /** the div that our map lives in
      * 
      * @type DOMElement */
@@ -212,10 +218,11 @@ OpenLayers.Map.prototype = {
 
         this.popups = new Array();
 
+        this.unloadDestroy = this.destroy.bindAsEventListener(this);
+        
+
         // always call map.destroy()
-        OpenLayers.Event.observe(window, 
-                      'unload', 
-                      this.destroy.bindAsEventListener(this));
+        OpenLayers.Event.observe(window, 'unload', this.unloadDestroy);
 
     },
 
@@ -223,6 +230,11 @@ OpenLayers.Map.prototype = {
     * @private
     */
     destroy:function() {
+
+        // map has been destroyed. dont do it again!
+        OpenLayers.Event.stopObserving(window, 'unload', this.unloadDestroy);
+        this.unloadDestroy = null;
+
         if (this.layers != null) {
             for(var i=0; i< this.layers.length; i++) {
                 //pass 'false' to destroy so that map wont try to set a new 
@@ -241,6 +253,10 @@ OpenLayers.Map.prototype = {
             this.div.removeChild(this.viewPortDiv);
         }
         this.viewPortDiv = null;
+
+        this.events.destroy();
+        this.events = null;
+
     },
 
     /**