(Ara) Replace two 2-valued params in VP with one 3-valued param.

* is copula / is have_V2 / is neither

There is no difference; all three options are is mutually exclusive. 
There 2 params in the first place only by accident. First one was added 
by AED 10 years agon, second by me only some weeks ago, without thinking 
that the params are mutually exclusive.

Also tested with gftest, no difference found after 2 hours of running.

src/arabic/QuestionAra.gf

@@ -14,7 +14,7 @@ lin
 
   -- : IP -> VP -> QCl ;      -- who walks
   QuestVP qp vp =
-   let np = ip2np qp vp.isPred ;
+   let np = ip2np qp (case vp.vtype of {Copula=>True ; _=>False}) ;
        cl = PredVP np vp ;
     in { s = \\t,p,qf => cl.s ! t ! p ! toOrder qf } ;