Multimap now conforms to other EventPane subclasses in expected behavior for

some functions, and has tests available, so when I break it at some point, 
hopefully I'll know :)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@1389 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/MultiMap.js

@@ -237,7 +237,8 @@ OpenLayers.Layer.MultiMap.prototype =
      * @type int
      */
     getOLZoomFromMMZoom: function(mmZoom) {
-        return mmZoom - 1;
+        if (mmZoom) return mmZoom - 1;
+        return null;
     },
     
     /**
@@ -248,7 +249,8 @@ OpenLayers.Layer.MultiMap.prototype =
      * @type int
      */
     getMMZoomFromOLZoom: function(olZoom) {
-        return olZoom + 1;
+        if (olZoom) return olZoom + 1;
+        return null;
     },
 
   //
@@ -326,6 +328,11 @@ OpenLayers.Layer.MultiMap.prototype =
         return pixel;
     },
 
+    destroy: function() {
+        this.multimap = null;
+        OpenLayers.Layer.EventPane.prototype.destroy.apply(this, arguments); 
+    },
+
     /** @final @type String */
     CLASS_NAME: "OpenLayers.Layer.MultiMap"
 });