[RFA] Mention 'set target-async' in NEWS.

[Eli Zaretskii]

> From: Vladimir Prus <vladimir@codesourcery.com>
> Date: Tue, 19 Aug 2008 17:17:47 +0400
> 
> 
> Is this OK?

Yes, but I'd only mention "set target-async", since the text below it
is not fit for the "show" command.  You could mention "show
target-async" in the text, something like

   "show target-async" displays the current state of asynchronous
   execution of the target.

Thanks.