NH-3777: Replaced NHibernate.Loader.TopologicalSorter by a more performant implementation.

- Because of a slight change in the (internal) Interface of TopologicalSorter, JoinWalker had to be adjusted (note that the removed parameter i was identical to the return value for the current use of the sorter)

Author: Akkerman

src/NHibernate/Loader/TopologicalSorter.cs

@@ -83,7 +83,7 @@ private void eliminateNode(Node node)
 
         private Node getNodeWithoutSuccessors()
         {
-            // note: It would be more performant to check the nodes in reverse order, since that would allow decreases of "_nodeCount" in "eliminateNode" 
+            // note: It would be more performant to check the nodes in reverse order, since that would allow decreases of "_nodeCount" in "eliminateNode"
             // as often as possible since high indices are preferred over low indices whenever there is a choice.
             // However, several test cases are violated if this change is made; It seems not all restrictions are properly added as edges here.
             for (int i = 0; i < _nodeCount; i++)