special keyword for silent wrong-code bugs

[Robert Dewar]

Paul Brook wrote:

> 2 is a IMHO fairly academic distinction. We either care about code working 
> (and support no-conforming code as an extension), or we decide that we're ok 
> with that particular code being broken.

That's a better way to express the concern I had. I would not get
excited about some obscure boundary test of some obscure standard
rule if it is unlikely it will be run into, but by contrast wrong
code for either an out-and-out extension, or a case where we could
argue that the "wrong" code is allowed by the standard, but really
it was a bug, are much more important if they are likely to affect
real programs.