[m-rev.] for review: Add some mvar predicates.

[Julien Fischer]

Hi Peter,

On Wed, 7 Sep 2016, Peter Wang wrote:

> library/thread.mvar.m:
> 	Add mvar.init/1, mvar.impure_init/1, mvar.try_read/4.
>
> 	Improve some documentation.
>
> NEWS:
> 	Announce additions.

That looks fine.

Julien.