Merge pull request #876 from bartvde/tilemgr-changelayer

the tileQueue is not always cleared, for instance when adding a layer in... (r=@ahocevar)

lib/OpenLayers/TileManager.js

@@ -183,7 +183,7 @@ OpenLayers.TileManager = OpenLayers.Class({
      * evt - {Object} Listener argument
      */
     changeLayer: function(evt) {
-        if (evt.property === 'params') {
+        if (evt.property === 'visibility' || evt.property === 'params') {
             this.updateTimeout(evt.object, 0);
         }
     },
@@ -425,4 +425,4 @@ OpenLayers.TileManager = OpenLayers.Class({
         this._destroyed = true;
     }
 
-});
+});