NH-3777: Reverted TopologicalSorter to initial commit (which was broken because not all constraints were available)

Author: Akkerman

src/NHibernate/Loader/TopologicalSorter.cs

@@ -83,10 +83,9 @@ 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"
-            // 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++)
+            // note: Check the nodes in reverse order, since that allows decreases of "_nodeCount" in "eliminateNode"
+            // as often as possible because high indices are preferred over low indices whenever there is a choice.
+            for (int i = _nodeCount - 1; i >= 0; i--)
             {
                 var node = _nodes[i];
                 if (node.Eliminated)