A new factor has entered the picture: the opportunity to move dialogs from using tk widgets to ttk widgets.  However, we cannot yet drop support for systems that do not have ttk widgets.  We could accommodate using both sets of dialog widgets by adding lots of conditional code within each file as needed, but that would only solve the ttk or not issue.

I decided instead to have separate files.  This way, the ttk files can have pep 8 names and style and refactorings. New files will be declared private in docstrings. When a new file is written, corresponding old files, if imported (by an extension or non-idle program) when ttk *is* being used , will raise a Deprecation Warning.  The same idea will be used for the text window files for shell, edit, and output, which badly need refactoring both as they are and to allow tabbed windows with multiple files.

Overall, the plan is to gradually add new files to all current versions (except, probably, 3.4) and delete old files in the future (possibly in 3.6, but not decided now).  The transition overlap will be messier than a simple rename, but will avoid the problems of patch merges and immediately breaking 3rd-party code.  And the result will be much more and much better than a simple rename.