D1 -> D2

[Walter Bright]

Bernard Helyer wrote:
> No. The contents of a version block is still parsed. If the D2 code 
> doesn't _parse_ as valid D1, then the D1 compiler will reject it, even if 
> the version block will not be processed further than that.

Yes. Now, if the D1 compiler is supposed to successfully lex & parse (and then 
ignore) false version blocks, it becomes impossible for a D1 compiler to be 
stable. It will have to track every future D language variant, missteps and all.