To string! none behaves differently than Rebol 2

To string! none behaves differently than Rebol 2

```
to-string none
```

provokes an error in RED (compliant with the conversion matrix and Rebol 3) but returns "none" in Rebol 2.

Maybe a difference to be added to : 
https://github.com/red/red/wiki/%5BDOC%5D-Differences-between-Red-and-Rebol#make-with-none

in the same section as Make with none.