Squeak 3.8.1: small warning for anyone using VMMaker

1. Start from a virgin 3.8 image
2. load the updates
3. save that as a 3.8.1
4. 'save as' your-typical-working-name
5. and load VMMaker again and save, of course.

[ANN] Squeak 3.8.1 by Tim Rowledge.