Refixed the homepage link and fixed the tests that were broken

- Added an ApplicationPath override to the StubHttpRequest

--HG--
branch : dev

src/Orchard.Tests/Stubs/StubHttpContext.cs

@@ -34,6 +34,10 @@ namespace Orchard.Tests.Stubs {
                 get { return _appRelativeCurrentExecutionFilePath; }
             }
 
+            public override string ApplicationPath {
+	            get { return "/"; }
+            }
+
             public override string PathInfo {
                 get { return ""; }
             }

src/Orchard/UI/Navigation/NavigationManager.cs

@@ -35,7 +35,7 @@ namespace Orchard.UI.Navigation {
 
         public string GetUrl(string menuItemUrl, RouteValueDictionary routeValueDictionary) {
             var url = string.IsNullOrEmpty(menuItemUrl) && (routeValueDictionary == null || routeValueDictionary.Count == 0)
-                          ? null
+                          ? "~/"
                           : !string.IsNullOrEmpty(menuItemUrl)
                                 ? menuItemUrl
                                 : _urlHelper.RouteUrl(routeValueDictionary);