FYI: Make Message.WRITE final (#38)

[Jaroslav Tulach]

### Tuesday 09 of February 2016, 09:37:20 @ jaroslav.tulach at oracle.com ###
> Hi language implementors,
> anybody minds if we fix this mistake and make the field final?
> 
> If so, please speak up in the request. Otherwise we integrate the change on
> Friday Feb 12, 2015. -jt
> 
> view it on GitHub

Here is the missing link:
https://github.com/graalvm/truffle/pull/38
-jt