[ATL] Implement CAtlList::AddHeadList and CAtlList::AddTailList

What about a convenient way to append CAtlList to each other?

sdk/lib/atl/atlcoll.h

@@ -483,6 +483,9 @@ class CAtlList
     E RemoveHead();
     E RemoveTail();
 
+    void AddHeadList(_In_ const CAtlList<E, ETraits>* plNew);
+    void AddTailList(_In_ const CAtlList<E, ETraits>* plNew);
+
     POSITION InsertBefore(_In_ POSITION pos, INARGTYPE element);
     POSITION InsertAfter(_In_ POSITION pos, INARGTYPE element);
 
@@ -639,6 +642,34 @@ POSITION CAtlList<E, ETraits>::AddTail(INARGTYPE element)
     return (POSITION)Node;
 }
 
+template<typename E, class ETraits>
+void CAtlList<E, ETraits>::AddHeadList(_In_ const CAtlList<E, ETraits>* plNew)
+{
+    ATLASSERT(plNew == NULL);
+
+    POSITION pos = plNew->GetTailPosition();
+
+    while (pos)
+    {
+        INARGTYPE element = plNew->GetPrev(pos);
+        AddHead(element);
+    }
+}
+
+template<typename E, class ETraits>
+void CAtlList<E, ETraits>::AddTailList(_In_ const CAtlList<E, ETraits>* plNew)
+{
+    ATLASSERT(plNew == NULL);
+
+    POSITION pos = plNew->GetHeadPosition();
+
+    while (pos)
+    {
+        INARGTYPE element = plNew->GetNext(pos);
+        AddTail(element);
+    }
+}
+
 template<typename E, class ETraits>
 E CAtlList<E, ETraits>::RemoveHead()
 {