This enhancement adds a warning message if someone tries to save over the
original "clean" downloaded image.  I think it's fair to say that it's not
generally recommended to overwrite the original image, since once you've
done that, you can't go back.  It's considered good practice to save the
changed image to a new name.  Beginners don't realize this, though, so the
warning message is useful for them.  (I've seen a few posts to this list
from folks asking how to get their original image back... gotta go
download the whole thing again.)

The enhancement works by comparing the current Squeak version (EToySystem
version) with the image name, and if they're the same (e.g. Squeak2.7),
then it brings up the warning message.  It doesn't bring up the warning
for alpha images.  (This shouldn't be much of an inconvenience to
anyone... once you've done a 'save as...', you shouldn't ever see the
warning.)

The changeset modifies only SystemDictionary>>snapshot:andQuit:.  (It's
compatible with the latest 2.8alpha, but not 2.7.)  It's available at:

http://www.mindspring.com/~dway/smalltalk/CleanSaveWarning-dew.cs

Here's the text of the warning (confirm:) message...

'You are about to save over a clean ', EToySystem version, ' image.
Normally it is recommended to use ''save as...'' first instead to save
your working image, so that a copy of the original (clean) image is
preserved.  Do you still want to proceed with saving?'

Any suggestions on wording, or appropriateness, are welcome.

- Doug Way
  EAI/Transom Technologies, Ann Arbor, MI
  http://www.transom.com
  dway at mat.net, @eai.com