show message on notebook list if server is unreachable

usefull when :
server goes down, you don't notice it on dashboard

restart on https, cookies is unvalid, autoreload don't work

IPython/frontend/html/notebook/static/js/notebooklist.js

@@ -88,19 +88,23 @@ var IPython = (function (IPython) {
 
 
     NotebookList.prototype.load_list = function () {
+        var that = this;
         var settings = {
             processData : false,
             cache : false,
             type : "GET",
             dataType : "json",
-            success : $.proxy(this.list_loaded, this)
+            success : $.proxy(this.list_loaded, this),
+            error : $.proxy( function(){that.list_loaded([],null,null,{msg:"Error connecting to server."})},this)
         };
+
         var url = $('body').data('baseProjectUrl') + 'notebooks';
         $.ajax(url, settings);
     };
 
 
-    NotebookList.prototype.list_loaded = function (data, status, xhr) {
+    NotebookList.prototype.list_loaded = function (data, status, xhr, param) {
+        var message = param.msg || 'Notebook list empty.';
         var len = data.length;
         this.clear_list();
 
@@ -109,7 +113,7 @@ var IPython = (function (IPython) {
             $(this.new_notebook_item(0))
                 .append(
                     $('<div style="margin:auto;text-align:center;color:grey"/>')
-                    .text('Notebook list empty.')
+                    .text(message)
                     )
         }