display cause of invalid feed (#580)

src/main/webapp/js/controllers.js

@@ -52,9 +52,11 @@ module.controller('SubscribeCtrl', ['$scope', '$location', 'FeedService', 'Categ
 						$scope.state = 'ok';
 						$scope.sub.title = data.title;
 						$scope.sub.url = data.url;
+						$scope.stacktrace = null;
 					}, function(data) {
 						$scope.state = 'failed';
 						$scope.sub.title = 'Loading failed. Invalid feed?';
+						$scope.stacktrace = data.data;
 					});
 				}
 			};

src/main/webapp/templates/feeds.subscribe.html

@@ -34,4 +34,6 @@
 			</div>
 		</div>
 	</form>
+	
+	<pre ng-if="state == 'failed'">{{stacktrace}}</pre>
 </div>