Finally fix SF bug #441172, using a variant of patch ##443626:

canceling an edit operation would not revert the value of the field.
The fix takes care to destroy the Entry object, as suggested in the
patch.

Tools/idle/TreeWidget.py

@@ -291,6 +291,12 @@ class TreeNode:
         self.canvas.focus_set()
 
     def edit_cancel(self, event=None):
+        try:
+            entry = self.entry
+            del self.entry
+        except AttributeError:
+            return
+        entry.destroy()
         self.drawtext()
         self.canvas.focus_set()