Tkinter Menu Item Activation

[MartinRinehart at gmail.com]

Tkinter definitely deserves more respect! I'm making rapid progress
and it looks good.

But am stuck on this: I want the File/Save state to change from
disabled to enabled, depending on whether or not there is something to
save (Text modified). Google returns results in every language except
Python.

Sub problems: how to change state of menu item? how to detect changes
in Text widget?

Help appreciated.