[Tutor] filtering listed directories

[Laura Creighton]

wxPython has a SHOWHIDDEN checkbox for turning exactly this on and off,
but if you wanted to exclude all .pyc files while leaving the rest
alone, I don't see a way to do that, either, right now.

QT has a ton of options including showing hidden files.

The common problem we seem to be up against is that the gui packages
really want to use the native OS file dialogs whenever possible, and
the people making such dialogs -- at least in some OSes, never
dreamed that somebody would ever want to exclude only certain files
(as opposed to only match certain files).

Laura