#5991: let completion for the "help" command include help topics.

This also simplifies the Cmd.get_names() method implementation; it was written
at a time where dir() didn't consider base class attributes.
diff --git a/Lib/test/test_cmd.py b/Lib/test/test_cmd.py
index 8898a32..2ee5cef 100644
--- a/Lib/test/test_cmd.py
+++ b/Lib/test/test_cmd.py
@@ -57,15 +57,17 @@
     >>> mycmd.completenames("12")
     []
     >>> mycmd.completenames("help")
-    ['help', 'help']
+    ['help']
 
     Test for the function complete_help():
     >>> mycmd.complete_help("a")
     ['add']
     >>> mycmd.complete_help("he")
-    ['help', 'help']
+    ['help']
     >>> mycmd.complete_help("12")
     []
+    >>> sorted(mycmd.complete_help(""))
+    ['add', 'exit', 'help', 'shell']
 
     Test for the function do_help():
     >>> mycmd.do_help("testet")