RFR 8188226: jextract diagnostic generation should be improved

[Henry Jen]

Looks good to me, thanks for adding copyright.

Cheers,
Henry

> On Jan 8, 2018, at 8:39 AM, Sundararajan Athijegannathan <sundararajan.athijegannathan at oracle.com> wrote:
> 
> Please review: http://cr.openjdk.java.net/~sundar/8188226/webrev.00/
> 
> * stack traces printed only on "debug" [when jextract.debug property is set]
> * default log level set to "warning" [user can change log level by -log option already]
> * added resource for localizing messages.
> 
> PS. Piggybacking to add missing copyright messages in few source files.
> 
> Thanks,
> -Sundar