[Tutor] New version of calculator.py

[Jesse W]

Hey ho-

	Here is the new version of the simple calculator I wrote for one 
of the Pyhon Challanges.  It now includes a zero button (thank you, 
Gregor Lingl), and I think the integer overflow problem is solved 
(thank you, Tommy Butler)

Copying from my previous message:
Any comments, suggestions, patches, gripes, or simple 
screams of emotion are welcomed.  Please only post to the list.

					Thank you for your time and support,
						Jesse W