show help switches when using help command without subsequent command.

electrum

@@ -287,7 +287,8 @@ if __name__ == '__main__':
     if cmd == 'help':
         cmd2 = firstarg
         if cmd2 not in known_commands:
-            print_error("Error: Command not found.")
+            parser.print_help()
+            print
             print "Type 'electrum help <command>' to see the help for a specific command"
             print "Type 'electrum --help' to see the list of options"
             print "List of commands:", ', '.join(known_commands)