relax SVN archive

Renamed all execute() methods to on_execute() and update() to on_display().

The calls to update() from execute() have been eliminated.

The on_apply() method by default now calls on_display().

Renamed the update() method to on_display().

Renamed the on_exit() wizard page method to on_execute().

Created the on_apply() wizard page method.

Fix for the ok wizard button - the method is now private.

Rearrangement of the wizard page methods and variables.

Many variables and methods which should not be touched by the derived classes have been made
private. The execute() and update() methods have been deleted. And the class docstring has been
updated to describe which methods should be over-written and which should be used.

Updated the Wiz_window class docstring.

Redesigned the wizard page so that on_exit() replaces execute().

Spacing fix in the File_selector.__init__() docstring.