Message 393166 - Python tracker

PR 25678 merged on top of the sidebar patch results in using space indents with the sidebar.  An additional patch is needed to have the mode with '>>>' on a line by itself instead of having a sidebar.

The shell prompt_last_line attribute is now obsolete (it is always '') and should be removed after uses, such as "if self.prompt_last_line" headers and the following code, are removed.