Rework bootstrap to support loading widgetset without application

WebContent/VAADIN/vaadinBootstrap.js

 	var defaults;
 	var apps = {};
 	var themesLoaded = {};
-	var widgetsetsRequested = {}
-	var widgetsetApps = {};
+	var widgetsets = {};
 	
 	
 	var log = function() {
 	}
 	
 	var loadWidgetset = function(basePath, widgetset) {
-		if (widgetsetsRequested[widgetset]) {
-			//TODO Tell the widgetset to load another application
+		if (widgetsets[widgetset]) {
 			return;
 		}
 		log("load widgetset", basePath, widgetset)
 		scriptTag.setAttribute('src', url);
 		document.getElementsByTagName('head')[0].appendChild(scriptTag);
 		
-		widgetsetsRequested[widgetset] = true;
+		widgetsets[widgetset] = {
+			pendingApps: []
+		};
 	}
 	
 	window.vaadin = window.vaadin || {
 				var widgetset = getConfig('widgetset');
 				if (widgetset && widgetsetBase) {
 					loadWidgetset(widgetsetBase, widgetset);
-					if (widgetsetApps[widgetset]) {
-						widgetsetApps[widgetset].push(appId);
+					if (widgetsets[widgetset].callback) {
+						log("Starting from bootstrap", appId);
+						widgetsets[widgetset].callback(appId);
 					}  else {
-						widgetsetApps[widgetset] = [appId];
+						log("Setting pending startup of ", appId);
+						widgetsets[widgetset].pendingApps.push(appId);
 					}
 				} else if (mayDefer) {
 					fetchRootConfig();
 				} else {
-					throw "Widgetset not defined";
+					throw "Widgetset not defined: " + widgetsetBase + " -> " + widgetset;
 				}
 			}
 			bootstrapApp(true);
 			var app = apps[appId]; 
 			return app;
 		},
-		popWidgetsetApp: function(widgetset) {
-			if (widgetsetApps[widgetset]) {
-				return widgetsetApps[widgetset].pop();
-			} else {
-				return null;
+		registerWidgetset: function(widgetset, callback) {
+			log("Widgetset registered", widgetset)
+			widgetsets[widgetset].callback = callback;
+			for(var i = 0; i < widgetsets[widgetset].pendingApps.length; i++) {
+				var appId = widgetsets[widgetset].pendingApps[i];
+				log("Starting from register widgetset", appId);
+				callback(appId);
 			}
+			widgetsets[widgetset].pendingApps = null;
 		}
 	};
 	

src/com/vaadin/terminal/gwt/client/ApplicationConfiguration.java

 import com.google.gwt.core.client.GWT.UncaughtExceptionHandler;
 import com.google.gwt.core.client.JavaScriptObject;
 import com.google.gwt.core.client.JsArrayString;
+import com.google.gwt.core.client.Scheduler;
+import com.google.gwt.core.client.Scheduler.ScheduledCommand;
 import com.google.gwt.user.client.Command;
 import com.google.gwt.user.client.Timer;
 import com.vaadin.terminal.gwt.client.ui.VUnknownComponent;
 
     }
 
-    /**
-     * Starts the next unstarted application. The WidgetSet should call this
-     * once to start the first application; after that, each application should
-     * call this once it has started. This ensures that the applications are
-     * started synchronously, which is neccessary to avoid session-id problems.
-     * 
-     * @return true if an unstarted application was found
-     */
-    public static boolean startNextApplication() {
-        String applicationId = getNextUnstartedApplicationId(GWT
-                .getModuleName());
-        if (applicationId != null) {
-            ApplicationConfiguration appConf = getConfigFromDOM(applicationId);
-            ApplicationConnection a = GWT.create(ApplicationConnection.class);
-            a.init(widgetSet, appConf);
-            a.start();
-            runningApplications.add(a);
-            return true;
-        } else {
-            deferredWidgetLoader = new DeferredWidgetLoader();
-            return false;
-        }
+    public static void startApplication(final String applicationId) {
+        Scheduler.get().scheduleDeferred(new ScheduledCommand() {
+            public void execute() {
+                ApplicationConfiguration appConf = getConfigFromDOM(applicationId);
+                ApplicationConnection a = GWT
+                        .create(ApplicationConnection.class);
+                a.init(widgetSet, appConf);
+                a.start();
+                runningApplications.add(a);
+            }
+        });
     }
 
     public static List<ApplicationConnection> getRunningApplications() {
         return runningApplications;
     }
 
-    private native static String getNextUnstartedApplicationId(
-            String widgetsetName)
-    /*-{
-        return $wnd.vaadin.popWidgetsetApp(widgetsetName);
-     }-*/;
-
     private native static JsoConfiguration getJsoConfiguration(String appId)
     /*-{
         return $wnd.vaadin.getApp(appId);
             }
         });
 
-        startNextApplication();
+        registerCallback(GWT.getModuleName());
+        deferredWidgetLoader = new DeferredWidgetLoader();
     }
 
+    public native static void registerCallback(String widgetsetName)
+    /*-{
+        var callbackHandler = @com.vaadin.terminal.gwt.client.ApplicationConfiguration::startApplication(Ljava/lang/String;);
+        $wnd.vaadin.registerWidgetset(widgetsetName, callbackHandler);
+    }-*/;
+
     /**
      * Checks if client side is in debug mode. Practically this is invoked by
      * adding ?debug parameter to URI.

src/com/vaadin/terminal/gwt/client/ApplicationConnection.java

                 public void onError(Request request, Throwable exception) {
                     showCommunicationError(exception.getMessage());
                     endRequest();
-                    if (!applicationRunning) {
-                        // start failed, let's try to start the next app
-                        ApplicationConfiguration.startNextApplication();
-                    }
                 }
 
                 public void onResponseReceived(Request request,
                     } else {
                         applicationRunning = true;
                         handleWhenCSSLoaded(jsonText, json);
-                        ApplicationConfiguration.startNextApplication();
                     }
                 }