Differentiated the z-index base of base layers versus popups.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1173 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -16,7 +16,7 @@ OpenLayers.Map.prototype = {
      * 
      * @type Object
      */
-    Z_INDEX_BASE: { Layer: 100, Popup: 200, Control: 1000 },
+    Z_INDEX_BASE: { BaseLayer: 100, Overlay: 325, Popup: 750, Control: 1000 },
 
     /** supported application event types
      * 
@@ -261,7 +261,9 @@ OpenLayers.Map.prototype = {
     */    
     addLayer: function (layer) {
         layer.div.style.overflow = "";
-        layer.div.style.zIndex = this.Z_INDEX_BASE['Layer'] + this.layers.length;
+        layer.div.style.zIndex = 
+            this.Z_INDEX_BASE[layer.isBaseLayer ? 'BaseLayer' : 'Overlay']
+            + this.layers.length * 5;
 
         if (layer.isFixed) {
             this.viewPortDiv.appendChild(layer.div);
@@ -288,7 +290,6 @@ OpenLayers.Map.prototype = {
                 layer.setVisibility(false);
             }
         }
-
     },
 
     /**