Issue #24225: Within idlelib files, update idlelib module names.

This follows the previous patch that changed idlelib file names.
Class names that matched old module names are not changed.
Change idlelib imports in turtledemo.__main__.

Exception: config-extensions.def.  Previously, extension section
names, file names, and class names had to match.  Changing section
names would create cross-version conflicts in config-extensions.cfg
(user customizations).  Instead map old names to new file names
at point of import in editor.EditorWindow.load_extension.

Patch extensively tested with test_idle, idle_test.htest.py, a custom
import-all test, running IDLE in a console to catch messages,
and testing each menu item.  Based on a patch by Al Sweigart.

Lib/idlelib/idle_test/test_config_sec.py

@@ -0,0 +1,75 @@
+"""Unit tests for idlelib.config_sec"""
+import unittest
+from idlelib.idle_test.mock_tk import Var, Mbox
+from idlelib import config_sec as name_dialog_module
+
+name_dialog = name_dialog_module.GetCfgSectionNameDialog
+
+class Dummy_name_dialog:
+    # Mock for testing the following methods of name_dialog
+    name_ok = name_dialog.name_ok
+    Ok = name_dialog.Ok
+    Cancel = name_dialog.Cancel
+    # Attributes, constant or variable, needed for tests
+    used_names = ['used']
+    name = Var()
+    result = None
+    destroyed = False
+    def destroy(self):
+        self.destroyed = True
+
+# name_ok calls Mbox.showerror if name is not ok
+orig_mbox = name_dialog_module.tkMessageBox
+showerror = Mbox.showerror
+
+class ConfigNameTest(unittest.TestCase):
+    dialog = Dummy_name_dialog()
+
+    @classmethod
+    def setUpClass(cls):
+        name_dialog_module.tkMessageBox = Mbox
+
+    @classmethod
+    def tearDownClass(cls):
+        name_dialog_module.tkMessageBox = orig_mbox
+
+    def test_blank_name(self):
+        self.dialog.name.set(' ')
+        self.assertEqual(self.dialog.name_ok(), '')
+        self.assertEqual(showerror.title, 'Name Error')
+        self.assertIn('No', showerror.message)
+
+    def test_used_name(self):
+        self.dialog.name.set('used')
+        self.assertEqual(self.dialog.name_ok(), '')
+        self.assertEqual(showerror.title, 'Name Error')
+        self.assertIn('use', showerror.message)
+
+    def test_long_name(self):
+        self.dialog.name.set('good'*8)
+        self.assertEqual(self.dialog.name_ok(), '')
+        self.assertEqual(showerror.title, 'Name Error')
+        self.assertIn('too long', showerror.message)
+
+    def test_good_name(self):
+        self.dialog.name.set('  good ')
+        showerror.title = 'No Error'  # should not be called
+        self.assertEqual(self.dialog.name_ok(), 'good')
+        self.assertEqual(showerror.title, 'No Error')
+
+    def test_ok(self):
+        self.dialog.destroyed = False
+        self.dialog.name.set('good')
+        self.dialog.Ok()
+        self.assertEqual(self.dialog.result, 'good')
+        self.assertTrue(self.dialog.destroyed)
+
+    def test_cancel(self):
+        self.dialog.destroyed = False
+        self.dialog.Cancel()
+        self.assertEqual(self.dialog.result, '')
+        self.assertTrue(self.dialog.destroyed)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2, exit=False)