new restrictedMinZoom property. r=bartvde (closes #3024)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@11058 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -1800,8 +1800,8 @@ OpenLayers.Map = OpenLayers.Class({
      *           within the min/max range of zoom levels.
      */
     isValidZoomLevel: function(zoomLevel) {
-       return ( (zoomLevel != null) &&
-                (zoomLevel >= 0) && 
+        return ( (zoomLevel != null) &&
+                (zoomLevel >= this.getRestrictedMinZoom()) && 
                 (zoomLevel < this.getNumZoomLevels()) );
     },
     
@@ -1905,6 +1905,20 @@ OpenLayers.Map = OpenLayers.Class({
         return maxExtent;
     },
     
+    /**
+     * Method: getRestricteMinZoom
+     *
+     * Returns:
+     * {Integer} the minimum zoom level allowed for the current baseLayer.
+     */
+    getRestrictedMinZoom: function() {
+        var minZoom = null;
+        if (this.baseLayer != null) {
+            minZoom = this.baseLayer.restrictedMinZoom;
+        }
+        return minZoom;
+    },
+    
     /**
      * APIMethod: getNumZoomLevels
      *