Remove tiles that are still loading at alt z

When zooming to a new zoom level, we can immediately remove tiles from the previous level.  This (strongly) suggests not adding images to the container until they have actually loaded.

src/ol/renderer/dom/tilelayer.js

@@ -153,6 +153,19 @@ ol.renderer.dom.TileLayer.prototype.handleTileChange_ = function(event) {
 };
 
 
+/**
+ * Remove all loading tiles that have been appended.
+ * @private
+ */
+ol.renderer.dom.TileLayer.prototype.removeLoadingTiles_ = function() {
+  for (var key in this.loadingTiles_) {
+    var tile = this.loadingTiles_[key];
+    goog.dom.removeNode(tile.getImage(this));
+    delete this.loadingTiles_[key];
+  }
+};
+
+
 /**
  * @inheritDoc
  */
@@ -175,7 +188,7 @@ ol.renderer.dom.TileLayer.prototype.render = function() {
 
   if (z != this.renderedZ_) {
     // no longer wait for previously loading tiles
-    this.loadingTiles_ = {};
+    this.removeLoadingTiles_();
   }
 
   /**