(Ara) Fix bug in ImpersCl

ImpersCl (VP -> Cl) used to check whether the VP is predicative, and
in the positive case, force the dummy subject to not be a pronoun.
This has been wrong since the time I changed prodrop rules in PredVP.

The error that followed manifested when the Cl was put in subordinate
position: the subject pronoun did not attach to the conjunction.
An example follows.

Lang: SubjS that_Subj (UseCl (TTAnt TPres ASimul) PPos (ImpersCl (UseComp (CompNP (DetCN (DetQuant IndefArt NumSg) (UseN girl_N))))))
LangEng: that it is a girl

Old LangAra: أنَّ ها بِنتٌ (wrong)
New LangAra: أنَّ &+ ها بِنتٌ (correct)

src/arabic/IdiomAra.gf

@@ -9,10 +9,10 @@ concrete IdiomAra of Idiom = CatAra ** open
  lin
 
   -- : VP -> Cl ;        -- it is hot
-  ImpersCl vp =
-    let it : ResAra.NP = case vp.isPred of {
-    		True  => pron2np (gn2pron vp.obj.a.gn) ;
-	      False => gn2pron vp.obj.a.gn } ; -- if no obj, Per3 Masc Sg chosen by default
+  -- "it is a girl" becomes "she is a girl";
+  -- "it is twins" becomes "they<dual> are<dual> twins".
+  ImpersCl vp =            -- if no obj, default Per3 Masc Sg
+    let it : ResAra.NP = gn2pron vp.obj.a.gn ;
      in predVP it vp ;
 
   --  : VP -> Cl ;        -- one sleeps